Tips for obtaining specific legendary characters?

I really enjoy using all the legendary characters in Three Kingdoms, so any information on how to obtain specific ones would be appreciated.

An example, Sun Ren becomes old enough to be a general turn ~~78~~ 87 I believe, so you can marry her into your faction. And I think Zhou Yu just joins at some point if you have Sun Ce (might be specific to Sun Jian faction start?) Thanks in advance! Edit: wrong number