Now I have a new problem with it in different game. I want to marry my ruler to countess of Tudbury Hall, but she divorces instantly despite of both of us being landed.
No idea. It could be bug or you aren´t considered to be high enough to marry her that way (unless you are duke or higher, in that case there is no reason for game to divorce you). One way to get her titles is to marry her younger sister, who will certainly stay married to you, make her a kid and then use combination of plots and intrigue focus to exterminate anyone higher in line of succession (I did that as Littlefinger...managed to kill Ned, marry Cat and kill Hoster and Edmure, so she inherited Riverlands...but before that, we already had kids, so she didn´t divorce me). I also guess that game doesn´t divorce you if you stay married to her for some time, even without kids. It does that just at the beginning of marriage.
Also, just one small thing: When marrying for inheritance, switch to seduction focus and seduce your wife. Yes, it is absolutely unnecessary, because you already have her and you may have kids too...but it is not about her during her life, but about you after she dies. When your lover dies, you get many options, most of them with 90% chance of becoming depressed and being allowed to commit suicide. Yes, it may be bad to leave your character with long reign and all kinds of good stuff for your kid, who may be really crappy, but you will prevent him from being controlled by stupid AI after he inherits his mother´s lands. And you will immediately have character with bigger land.
Oh, one more thing: During megawars, everyone becomes independent...so when your wife dies, your heir won´t inherit, but it will go to your other kid (or vice versa, your heir will be disinherited from your lands and will get only hers, while your other kid will be your new heir). This is due to external inheritance laws...which make no sense in megawars, but creators of this mod had to work with CK2 mechanics that weren´t built for megawars. So, if your character dies and your second kid will inherit instead of first one (or your wife or whatever), just use console to fix it by giving your real heir lands he should own and switch to him.
