Liu Qi: From the novel, it seem that he was a completely useless and but did guard Jiang Xia and also involved in the battle of ChiBi. Historically he was no morethan Liu Bei's puppet, basically he was given mediocre rank/title and sit-out his whole life without doing anything...
Liu Zong: Novelwise, Liu Biao already believe that he was a brighter son than Liu Qi, and Liu Biao already wanted Liu Zong as his heir before Liu Bei's selfish JingZhou's ambition make Liu Biao re-think. Even in the novel, there are some sign that Liu Zong although young but a smart kid. I couldn't find anything about Liu Zhong in the book of Shu so I can't really comments on it, I've readed some other person post that Liu Zong was not killed by Cao Cao and infact Cao Cao actually allowed him become a protector or governor (but don't quote me on it).
Liu Bei: Novelwise, always claimed that Liu Biao wanted him to took over JingZhou, which is very hard to believe consider that Liu Biao was shock by one of Liu Bei's outburst. When Liu Biao told him that he wanted Liu Zong to succeed, Liu Bei did everything to stop it knowing that Liu Zong would not easily be his puppet. After he got crushed by Cao Cao and needing the assistance of generious Wu to have a piece of land, he always use this nephew (~cough) as puppet to get what he want in JingZhou. He imprisoned Liu Qi in Lust and Luxury, but Liu Qi was too weak and died because of the punishment.
IMO, only LIU BEI deserved to be the heir to Liu Biao with all the effort he did by screwing up and controlling the two of Liu Biao's sons..



