1.After the faction leader dies most of the faction without a heir at the start will be inherited by faction leader's wife, which in the history is not accurate at all, not to mention most of the wives are made up characters, not existing in real history
2.Making wife "relative" cause the game to link all her relative and her relative's relative as your relative, I can't marry my son to the widow of my other son's wife's cousin because appearantly that is incest.
3.They are just not historically accurate. Most of the women never participate in battle during that period, let alone ruling. While I agree some of the female has the power to rule (eg Lady Wu) or fight (eg Zheng Jiang), that shouldn't apply to wives/daughters of all the faction leaders.
4.There are just to few of females. They don't generate from recruitment pool, and in the late game there will be no one to marry to, and on top of that you can't marry two ppl unless one side is your relative (so ppl like Guan Yu, Zhang Fei are single forever unless you make them Liu Bei's "son"). There should be a decision to "marry" your male family member or non-relative generals in the family tree tab, marking them "married" but not generating a wife character. They can no longer be married to someone else and will occasionaly get son/daughter like a married couple in this game.