How does it work? Can I get them to form their own clan?
It doesn't work yet; No, you can't and probably won't ever
Marrying - yes. This 'probably won't ever' was meant for making them forming their own clanAw don't be so negative.
I believe the devs said you'll be able to pretty soon.
However I'd love to be able to marry the youngest 2 siblings in another family.
Them getting base noble gear and base skills for leading parties/governing into other families.
Are they actually functioning characters?