RandR

Li:
Ever wonder what the entire story is with Li?
Well, Clow Reed's Mother, (with the maiden name Shoran) Was a strong magician in her own right, and she lived in Hong Kong. she married an englishmen with the name of Clow, thus having Clow Reed. As kero explained, magic is just something anyone can do with practice, wich was what the Shorans normally did. But Clow Reed made his own magic. A very different magic. His own cards.
After he found no use of the lazen board, he gave it to his mother. It was passed down in her family, and eventually was passed on to Li, the youngest heir to the legacy. Since Li's mother is very much like Clow Reed's Mother, she wished to keep the Shoran blood in their family. But as I said, their magic was just like a recepie. You can only make it if you follow directions. That is why Meiling didn't posess the power of the Clow.

Fujuitaka (AKA Aiden)
Aiden was half of the re-incarnated Clow Reed. When Clow reed died, he knew that he would have to assign the cards to a new master. But he allowed himself to re-incarnate in order to aid the new master in the future. Aiden was the one half. If you don't belevae me, look at the simalaritys in Yukito, Eriol, Fujitaka, and Clow's faces while they smile and close their eyes. That's because Clow made Yue in likeness of himself, and the fact that Fujitaka and Eriol ARE clow reed makes sence also. Fujitaka had two kids. Sakura And Tori. Tori had some powers too. He had the power to see ghosts. Sakura gained the power of the clow magic. To obtain the cards, and to also sence spirits near by.

Eriol (AKA Eli):
Eriol was the other half-reincarnated person. Eriol looks more like clow, and he has some memories of Clow's past lifetime. His protectors are Ruby moon and Spinner Sun. (just like Sakura has Yue and Keroberos) Eriol's mission was to give sakura a reason to transform the cards. Eriol's power from clow was his staff, the protectors, and the power to control the elements and to posess people and things. Ms. makenzie trained Eriol over in England to be ready to aid Sakura in any way.

Tomoyo and Sakura:
Tomoyo and sakura are second cousins. Nedeshico (Sakura's mom) and Sonomi (tomoyo's mom) where cousins, and very close like sisters. Tomoyo had moved to Sakura's town, but sakura was unaware that Tomoyo was her cousin until Sonomi confrunted Fujitaka for the first time in ten or so years. Tomoyo knew it all along though. I wonder why.... ^_~