Way to raise vassal clan tier?

Is there a good way to raise the clan tier of your vassals?

Obviously it’s not a simple button I can hit (on console, not planning on using cheat menu) to make this happen but I’m wondering if there’s a good way to go about this?

I recently broke off from Vlandia and I took about half its territory with me. Like pretty much half of their Battanian holdings and then everything else is mine and they’re stuck with what they started at. As such I have 8 towns and had 18 castles. I promoted 8 of my old companions (so that my sons can take their positions and) to fill out my kingdom’s roster.

I’ve had promoted vassals before and even saw one raise its clan tier over a very long time and was maybe hoping there’s a good way to shorten how long it takes. In the past I gave that vassal a daughter to marry, so I did that with my top 3 commanders upon promotion and also all 8 got a cash gift of 1M denar.

So I’m out of daughters to marry off. I have more castles to play with but I was planning on doing this run by maybe only promoting wanderers and was thinking of filling in half the remaining castles this way. I have an absurd amount of granddaughters already but that will take a lot of time.

Do I have to be unselfish and give up those towns? They are giving me a loooooot of money everyday as well as influence. When I left Vlandia I had over 30k influence. I want to be able to veto anything so my goal was to keep the towns and not let anybody get significant holdings until much further down the line, but I could see that getting in the way of a clan rising tiers.

Any suggestions would be good or just thoughts on this kind of playstyle in general. The onexvepriok I’m thinking of making is inviting my in-laws clan to join but I had a wife die and got remarried so that’s awkward because maybe I should invite both lol?