Short of avoiding them altogether, ignoring all religious debate, I used a behavioral technique that worked on my parents when they kept accusing my kids every time I visited them.

It's simple..when people are doing what you want..speaking of neutral subjects, getting along, being kind and thoughtful, pay attention to them, laugh and talk with them, look at them, and engage.

The moment they start to veer off and snipe at each other, attack or insult you, etc., stop noticing them. Seem distracted, murmur "Um-hum," as though to a child, then say something about having to do something, and leave the room.

Go somewhere else and when you finally return, repeat that reaction each time they try to become abrasive. It doesn't take long to train them to behave around you.

I had an ex-wife with very devoted Jewish parents, even so much more than youd usually find as her dad was a figure-head for their church, led bible study groups, etc. It was very.. condescending, is the only way I can put it in to any word.
I knew that her parents didn't like me for a multitude of reasons, as between me not being religious, along with being white(she was full hispanic), and not being a wealthy/successful guy in their eyes, among a few other things.
I TRIED to be "open" to learn about their beliefs, give their church a try, all to try & connect with them and show how serious I was about her(the ex-wife) as well, but I'd just find hate, antagonism, and "the God band-aid" for everything... even when she had cheated or fooled around... God & prayer was the answer to it all for them, it was very delusional how it was their answer to everything.
I will say that I didn't hate them, but I did hate their means of God for every excuse. It was kinda pathetic & sad that they had an excuse or way to blame things on others through God, but when I'd suggest solutions to some more simple things, I'd be shrugged off. I eventually stopped trying, honestly... stopped caring to try so much.

It all depends on if you want to keep the peace or you want to speak your mind. If you want to keep the peace then I agree with what you agree with in front of the people . If you want to speak your mind and speak your mind but beware of the backlash. I've done both in the past but I prefer now to speak my mind.

I ignore them

I have a huge family with people ranging from ultra-left to ultra-right politics, atheist to born-again religion, and emotionally mature to utterly self-centered narcisism. With all those mine fields, I find the easiest way to deal with folks is to always remember that fundamentally, wherever on these spectrums an individual lies, people are generally well-intentioned. When someone says something that gets my dander up a bit, I bite my tongue and remind myself that they are a good person and mean well. Sometimes a smile and changing the subject are good enough to get past it. When that doesn't do the job, a little gentle honesty with a healthy dose of respect for their viewpoint usually does.

My former in-laws by prior marriage were those rare evangelical Christians who were actually very good, kind, generous people who were not quick to judge. They DO exist. Such people, religious or not, are always easy to accommodate. In fact, much more so than my current in-laws, who are not religious but are judgmental, paranoid, borderline personalities and all around assholes.

I find fire is most effective.

I fought for years with mine, then when my Father in Law was diagnosed with early onset althsiemers and his wife became wheelchair bound all in the same few months I got really close to them, I visit most days and handle their day to day financial management, help with their shopping and independence needs and spend a lot of time actually talking to them.
Actual problems put relationships and differences in perspective she still thinks I might go to Hell but is now willing to put in a good word for me when the time comes.

I don’t as I was very different from my 2nd wife’s family, they were fox watching WASP supremacists, using vulgar terms to discribe all minorities include me the kike not in front of me. It was the fervent belief the Christians still have a “ manifest destiny”. I tried them cordial at best and shared nothing it was a matter of no trust. And as I’ve said why enter a battle the is unwinable

The only in-laws I have that are religious are in Australia and I live in the US. Married couple, xtian and Jewish. They're not crazy boisterous about it but, they were offended by my kids poking fun at Christianity. One in particular. He had to be the most well read 15 year old athiest in the globe. He's evangelical about it. My wife is a devout xtian. My daughter is agnostic and my other so is a foxhole xtian. I have some cousins that became insane LDS members. I'm sure their dad is rolling over. He was at least agnostic. Other cousins that are ridiculously Catholic and have tithe more than I'll ever make.. Then, there's a TX clan that found God when the moved there. If you're looking for God, Jeeeezus in particular, I'd start in TX.

I have 38 first cousins. 33 of us grew up within 10 miles of each other. We were very tight as children and teenagers. But later in life, God got in the way. My grandfather told my mom she could be any religion she wanted as long as she was Democrat. So the way I had to deal with it was to block them on all sites. Its very sad for me. Most of the Catholics want to Catholic schools and performed all the rituals to please the priest and get on a hiway to heaven. My answer is of no help but it took me 20 minutes to text at sloth speed so I'm sending it anyway.

When you, or I , or anyone is confident in what they are you will be arrogant what to do. There is no need to compete , or to justify!

I'll literally talk with anyone on any topic, so far it's usually religious people who abandon discussions with me.

It's also best to just play nice with people I have to hang out with and encouraging people to face their delusions will rarely be effective. I frequently talk politics with people who disagree, but rational exchanges on religion are more rare.

I'm rarely antagonistic and have had outstanding conversations with a handful of theists. Simple questions if someone is being pushy usually gets them to abandon the discussion.

Why did several societies (including Christianity if people READ their damned book) transition from polytheism to monotheism?

Most religious people just have FAITH, FEEL they're right. So I ask how would an objective person pursue truth if confronted with many disparate people who all base their beliefs on faith, feelings...

People often whip out CS Lewis Mere Christianity, but "morality" has evolved a ton over time and mostly that boils down to pragmaticism. At some points in various societies it was moral or even required to have sex with other peoples' spouses to maximize the chance a society would survive. Other societies had less risk of extermination/inbreeding and fidelity helped bind people together. lol I can on and on and on here and that's why devout people generally run away screaming instead of whipping out their sacred texts.

Well my middle child is s religious 1st Baptist, they proselytize my grand children , which I get a little upset! I normally keep silent don't respond to their comments!

Divorce. But more seriously, while I was married, my inlaws weren't big on religion. There was one cousin who married into that family that was a preacher, but I only saw him once a year at the most. Good luck with your crew, sounds interesting.

I would just ignore it all

It's been decades since I realized that an entire branch of my family was never going to respect me, because I turned my back on their religion. Try to ''rise above,'' and divert those uncomfortable discussions. "One of the things I'll never discuss, Auntie Pious, is religion. Let's talk about recipes...." Or something.

I tie rocks to their feet and throw them into the nearest pond !!

I have cousins who have gone off the deep end. The cousins do not talk with one another; one of them won't talk with me (I said ted cruz was an idiot, and that crossed some boundary). I know of no way to get them to speak to one another. i have spoken/messaged both sides, It fascinates me that the "religious nuts" are less willing to meet to work out their differences. Neither side admits to knowing what the crux of the matter is, but it is clear to me that the snowflake is the religious nut.
You are in a more difficult position; it is easier for me to not get caught up in their emotions.
It is possible to remain on good terms with each side and wait for opening to suggest any reconcilliation and keep those suggestions low key & without any promise of success.
Expect nothing, but be open to aid if asked.

My dad is christian my mom was jewish there families got along

By coincidence my sis-in-law tried to "save me" this past Sunday, Lol.. I was returning from a trip to the country and stopped by their house to visit. My brother wasnt home so i sat down & talked to her for a while. She had a cross on a necklace and cross earrings which I thought odd but she's very religious so I didn't give that much thought. We talked for a while about family and then she started talking about praying for me, and I needed to accept god before it's to late. I told her I didn't need a god or believe in god. She said, "but what if it's true?", and I said, "What if it's not?". At that point I picked up my phone & sunglasses preparing to get up and leave and she apologized and said she'd drop it. I replied that she needed to and said, "No politics, no religion!". Lol.
I love Wanda, she's been my sis in law for 40 years but I'll never be religious and narrow minded like that. FWIW..

I have sort of inherited in laws - my son in law's parents - Every time I went to see my daughter and her husband we got shipped off to experience shabbat - With all the explanations - It was merciless- It was a while before I got the guts to say no I wasnt going.

Dead.