Regarding kids, I believe it's been in another comment before, but you can apparently not get any more kids with the same wife until the previous kid has grown up
Well, having Zhongda as a sworn brother means no brains can beat him. Just never ever plot to kick him out. Also, starting with "impregnating our wife" is peak sigma energy at this point. Well well, can't trust Cao Mengde after all. It's fine, time to remind the Hero of Chaos of the taste of defeat.
Not sure if it's been brought up yet (tried scanning through the video to double-check before commenting), but for boosting Cao Cao's relation (or any other hostile character), you should just need to select the "Reward or Punish" option during Parliament and reward him with a gift item there. The game forces him to accept it and it should boost the relation up to at least disinterested so you can start talking to him. I've done it a couple of times in my games with former antagonists I hired like Meng Huo and Deng Ai. I hope that helps (in the future at least, since Cao Cao went all Cao Cao already)!
Yeah after playing more of this game it seems synergetic officers will always give +5 minimum to all as deputies, so putting 2 wives as deputies will always be +10 to all your wife actually gave +5 +5 +6 but the 1 was removed but the +5s remained XD
Game says you could recruit Zhang Lu (Governor) and succeeds, maybe try for the science once. Curious to see whether you will got a free city or not if you recruit him