Ah, the things I do when I'm bored. Here's a diagram of the family tree from Tsubasa RESERVoir CHRoNiCLE/xxxHolic/Cardcaptor Sakura. Good luck understanding it (I tried not to cross too many arrows).
Key:
Blue name - male
Pink name - female
Number - which universe the person is originally from
Maroon arrow - romantic relationship
Red arrow - points from parents to child
Orange arrow - points from original to clone
Light blue arrow - points from deceased to reincarnation
Light green arrow - points from adoptive parent to child
Watanuki you might have noticed is a special case. He was created by the magician Clow Reed (green arrow) to be a dimensionally equivalent replacement (*not* a clone) of Syaoran (grey arrow) since Syaoran was making a permanent move from universe 2 to universe 3, and then was magically inserted into universe 2 so that he had always been the son of C!R!Syaoran and C!R!Sakura.
To make it worse, at the end of the story Fei Wong Reed, who created the clones of Sakura and Syaoran, dies at the end of the story. And, when a clone's creator dies, the clone also goes. But in their case the clone never had existed in the first place. Which means their reincarnations, who are treated as the same person essentially, also never had existed. Which, you may note, ends up leaving Syaoran and Watanuki springing forth from nothing. In fact, they now threaten the stability of the entire multiverse just by being. Fun, huh?
Finally, as food for thought, if Syaoran is dating the original version of the girl his mother is a reincarnated clone of, is that incest, and Oedipus Complex, both, or neither?