Unless you are in charge of this celebration, I would just come as you are...to what ever place the people in charge have arranged! There is no more need to prove to any of them... your worth and acceptance than if you were Catholic, a Muslim or any other religion, really! Non-believers may be the minority...but we still have the same value as any other human being has on this earth. So you can show up and be thankful to that grandmother...because, 'by hook or by crook'... she gave you some useful DNA, that help give your life more meaning! The rest of your clan, can do the same thing!

I am a retired ordained Lutheran pastor who is now atheist. But at times, I bite my tongue. Do it for your mom.

To answer your question about coming out as non religious I was comfortable about it because I was finally comfortable with myself and with who I am. You are concerned about how they are going to feel about you and how they feel or think about you and that my friend is none of your business. You shouldn't be worrying about that not one darn bit.
First of all whatever your belief is, that's yours not theirs. And your belief is only one part of your total being. It's not the total of who you are.
My friend put all the religious stuff up on the shelf and go participate in your mothers celebration. It's about celebrating her. It's about family. What church it happens in is not an issue.
Please get to where you see yourself as you are... the wonderful caring son who loves his mother. And start working on your self worth. Get to know yourself and fall in love with you!😘👍

you might smote your grandma!! be careful. what's the hurry ?

I got what is wrong with you, you must have a mental illness. I stoped worrying about what beople thought about me long ago. Have had girlfriends in the past because they were of the religous nature some of my family had hoped that they would lead me to their thinking. Do not think so.

For a long time, I have simply explained that nature is my "church" and that I practice what I believe in every action of my day, rather than having to go to a special building.