I think religions only exist in the physical realm. In my opinion, spiritual life on the other side doesn't have much to do with religious belief on the earthy side. In other words, religions give comfort to the physically living, but the dead/unborn are living a purely spiritual life, so they KNOW the reality. They don't need dogma, rules, ritual etc to assist them on the other side because it's an everyday reality. They walk continually in the knowledge of god/spirit. When they are reborn to the earth, they choose a family based on what they'd like to learn or who they'd like to be with.
Religion may be one of many deciding factors/options ~ along with economic class, gender, orientation, race, health status, location (in Canada or Afghanistan or Japan etc.) etc.
None of my past lives were within my family (with members of my present family). However, my best friends daughter we are pretty sure was her grandmother ~ the little girl has all the mannerisms and quirks of her great-gramma! I definately consider Kristen to be the reincarnation of her great-gramma; that's my example of familial reincarnation that I've experienced.
My other best friend (a Christian who otherwise scoffs at my New Age-ish beliefs) insists I was her brother in a past life. Curiously enough, *I* don't remember that, lol. I just take her word for it, LOL, because she cannot be convinced otherwise. I am beginning to think she wasn't my brother, though, but my beloved servant. No matter where we go or what we do, she falls a step behind me, like a servant would. If I slow down, so does she. If I speed up, she speeds up to be a step behind me. It drives me nuts! It's like she's "got my back" covered. She won't walk BESIDE me. She has no idea she does this, lol. Other people have noticed this, not just me.
I do think I've been reincarnated with a large "familiar group". None are biological family. All are friends or the children of friends or lovers. My friend Tiffany was a friend to me in an English life in the 1400's. My two best friends were nuns with me in Italy around 1100. My former lover was my wife in Russia at the turn of the Century. Another friends' child is very familiar (she is 3 now) and she adores me, but I can't quite place who we were to one another in some past life. I just "know" I've known her previously.
Not all of MY lives have been fortunate. In fact, only one of the four I remember for sure was nice and I have glimpses of one more that ended poorly, too. The 1100 Italian life, I was raped by soldiers who subdued our town, and bore a son in shame and took care of orphaned children at a monastery. In 1400 as an English midwife, I had a nice life and lived to old age and died in peace. In 1918, I was a Russian cavalry officer, my wife died in childbirth and I was assassinated in a coup, shot in the temple turning a corner. The other life I glimpse, was in Africa and I was a very dark black man with a wife, and we were watching another tribe hunt us in the forest. I don't think that one had a happy ending.
I love talking about past lives, though I like my present one pretty well!