Generals and Family members?

[praetorians cavalry]

Hi I've just started my first campaign a couple hours ago and I noticed that beside the family members like in RTW, I could also use the "generals" to command armies and govern provinces. Those generals have command stars, piety... just like family members, however I couldn't seem to recruit any new generals apart from the ones given at the start of the campaign. They don't have place in the family tree, too. So I'd like to know what are their roles in the game and how can I have more of them? Thanks in advance.
Ps: sorry one more thing: am I still able to adopt captains who win battles?