I have shared a couple of past lives with my son.
Here's what I've picked up:

1) I was my son's twin in one life. Our mother abandoned us on the river as infants. My son can not forgive our past life mother.

2) My son was also my sibling in another life.

3) My son was again my son in another life where I was his father and in this lifetime, I am his mother.

Yes, relatives can reincarnate into the same family.