A lot of it is probably random, but there have been studies where people have been born into the same family/family line. I personally think my youngest is my grandmother reincarnated (long story). So it can happen, though it's probably not a common occurrence. Carol Bowman has written a good book on the subject
Return From Heaven, that is worth checking out.
As far as recognizing people from past lives, that's a toughie. If you do a lot of regression work, then you may start noticing that you recognize people from your past lives, present in your current life, However the average person, probably wouldn't know. I think that often when we meet someone that we have an instant connection to (the old "I feel like I've known you forever" feeling), it's possible that there is a past life link. The same if you meet someone that you instantly hate/fear (or any other strong emotional reaction) for no reason at all, it could be a residual from a past life.