First, there's some wiggle room -- everyone finds their own level, but that level shifts with changes in consciousness, and emotional states such as love (which is an astral phenomenon) have considerable energy on the astral plane. You may well meet your grandparents in the immediate aftermath of death, but you may not stay with them indefinitely unless you're at a common level of consciousness.

As for reincarnation, yes, that's an issue. Back when there were fewer human bodies to fill with souls, that was less of a problem -- it was normal for people to spend a century or more between incarnations -- but these days, yeah, you may miss meeting someone for a while. It'll all straighten out as the population drops.