I've never really had anyone push and push and push. I have several family members who are not on speaking terms, and basically no one wants to be discussed to the "enemy," but occasionally people come up, and I'm just vague as I possibly can be.
How's Joan these days?
What's she up to?
Not much, work, hobby.
I heard something-or-other.
Yeah. I don't really know any details.
Lot's of I don't really know any details. Or I haven't talked to her in awhile. You would have to ask her about that, I have no clue.
Having someone ever so curious about why you and your sister haven't talked, you could just simply say, "I don't know, I guess we've both been busy." Just vague responses, and "I don't know," has typically worked for me, but like I said, I really haven't had anyone keep pushing and pushing and pushing. Usually they get the hint or I can escape the situation, say I'm going to go get a refill, do you want one, or something. Conversation over.
Really at this point it's no mystery the things that have happened that caused the divisions in the family. There's really no point in rehashing everything now, and who wants to bring up ugly topics at a family celebration anyway? I wouldn't have a problem saying I don't want to discuss it. Lots of stuff, I'm sure, if they really need to know, they can just ask that other person.