Can't destroy faction - fix?

[VirtualNight]

Whatever I try the result is always the same, the current king never goes oversea and the faction never dies, it actually keeps spamming attacks on my villages.

Stopping them is useless, there are like 20 lords switching factions each day and some go to the one I want to eliminate, also the "put the king on prisoner" fix seems a fake statement? I can't put him there, the option is greyed out, but i can put in anyone else. And yes, it's in my town and I had built the prison tower.

 

So, what I already tried:

 

• waited a few months
• captured the king (he stayed in the party), then sold him
• captured the king (he stayed in the party), then he escaped
• let the faction take back a castle, then i took it back
• offer peace
• offer peace, then declared war

 

 

I dont think it matters but I add that the current king is a claimant, as that was the only possible path to become a vassal as a female.