Since I suck at subtlety (so much so i was told i am as subtle as a heart attack aka not at all) I would be direct. Even if I tried to word things gently and in a roundabout way my facial expressions would give away what I was thinking anyways. I can never play poker dammit! >: o

Excellent suggestions already given here. I would also add, just reaching out to them and saying you would like to be more connected, how could we do this. Be open without expectations, just be prepared that you my not get back a response you would like. I know that's the hardest part but the most important; family dynamics make it particularly difficult. There are members of my family I rarely speak to; some have drifted away, some are just too difficult to have more than a superficial relationship with, and trying to change that is very frustrating. Just have to put it out there and then let it be.

I say, come to the point and ask. Clear the air. It maybe nothing but bad or lack of communication, then again, you might get an answer.

This has got me thinking. I got along pretty well with my step siblings but it's been almost 50 years since we were living together (or even remotely near each other) and beyond family events focused on our parents (and seeing them at those is incresingly rare) the odd FB interaction is about it.Our lives simply don't have any points of interaction and now that our kids ( our firstborns were just months apart) have grown there's not even that. Suddenly the separation doesn't feel so strange.

Perhaps instead of asking why, ask how. How can we become closer? I’m willing to try. The why will come up but if you’re showing a good faith (no pun intended) effort to build a new relationship despite whatever happened in the past, that might woo them. You’ll need to be prepared to hear “no” though.

I suggest that you post a letter to them (not email) individually prior to your October visit. Say that you look forward to reconnecting and getting to know each other again. Provide details of where you'll be lodging and when you will be available to meet for coffee (a meal is too much). Then it’s in their court. Don’t distress if they ignore the invitation: a genetic connection doesn’t guarantee a connection.

From your post, and some of your replies to other commenters it seems clear that you at least want to know what the problem/issue might be. My guess is you also would like to have a meaningful relationship with your sibs, which is normal. Since, in the 21st century, being connected to family is easier than ever with social media platforms (and FB has evolved into something that really caters to this, allowing you to share and connect with family and friends), I'd say there is definitely something more to this than simply having grown apart because of geographical distance. Like you said, how hard is it to return a phone call? Or how hard would it be to connect on FB and communicate there, sharing important family activities. It seems your relationship with them can't get much worse, so I don't think there's anything wrong with being direct here. You can use the niece's wedding as the basis for your concern.

I hope this helps.

I've found that moving far from family can do this. You cease to be part of the day today life they are in. And, as parents age, the become somewhat of a burden that you (and me) are too far away from to have to deal with as they do. Can breed resentment. And really, you have to ask yourself, as I did,if they weren't relatives, is there enough overlap in your lifestyle for them to have become your friends?

Let it go. You've made a life, and any reason they have is likely to be ill-formed and poorly thought through. They can come to you. There is no law that you have to get along or even be close to them because you have a biological relationship, which you don't control. You do control who who choose to be your family and friends.

I'm betting you did nothing in particular and that your answer will be just that.. "You did nothing." or even more frustrating will be.. "I don't know." It is more likely this is just how your family relationship has evolved over the past 20 - 30 years. This lack of interest in you just is. The situation is normal. It might be they have gotten so used to dealing with their lives without your inclusion that they don't give you a second thought even when you are in the room.

Whenever I run into a situation where someone I have been friends with or somewhat close to stops interacting with me I also wonder "what did I do." . It is a natural reaction of a person who cares for the feelings of others but it also points a finger to my own insecurities that need attention as well.

Instead of asking , "What did I do?" maybe approach it from a "How can I be more involved with you from now on?" Good luck!

I’m so sorry. It’s very hurtful when people change towards you. How was your relationship growing up? Was there closeness that evaporated as you each left home? It might be, they saw your moving away as a rejection, so it’s about how they feel, and out of your control.
If I were in your shoes, I’d be gentle but direct. Tell them you are still puzzled and your feelings about the disconnection, then ask if there’s a reason. Meet the answer with an open mind.
I recently had a terrible fight with my brother, in which he said some awful things to me. It sounded as if he had hated me for years. Once the dust settled, I found out that HE believed I disliked and disapproved of him. We’re working to repair, slowly...he’s a believer as well as politically conservative. At least, the confusion has been cleared away.
Good luck to you!

Difficult but try family is a complicated thing my sympathy