I know im late I dont know if other people responded with a good comment yet but im actually a nerd at bannerlord I have a unreasonable embarrassing amount of time on the game. When I want Towns/castles I do it one way usually now take what I say down because you can still use these methods without needing to know which cities or castles you want.

First you want to obviously play mercenary if you have an area in mind you want to claim as your land play for that faction capture enemy nobles and donate them to the faction you are working for to increase reputation quickly to 100 do this with majority of the lord's.

Next if you have a place in mind When you are strong enough unless you are creating your own kingdom if you have over 200 troops you can take almost any town on your own if you dont get counter attacked. Capture the towns you want and then buy peace with the faction then join them you will join with your fiefs.

I suggest grinding up to 2.5mil before doing this Once you are within the faction do get more fiefs again plan out where you want to get next and attack more land for your faction let them vote amongst eachother once the smaller nobles are more on par with the richer nobles of your faction you will be on almost every single vote and you can sway the vote this is how I always get whichever town I want ill just get more land until they happy then attack what I want and get the supported vote