Can i marry a lady vassal?

So, I've been playing some mods in which there are lady vassals , and id just like to know if they are marriageable.
If yes, what should i do?

In most new mods, not all, they add the ability to marry a Lady Vassal. If i made Ymira, for example, a vassal, i just talk to her, "i wish to ask you something" and click "create an alliance with your house" (like you do to a man vassal for his daughter" she will suggest that you and her get married, and if she likes you, or are king, she will say yes and make a feast.