Hmm personally I think the parents/family are trapped. That baron vassal most likely do everything in order to make her father can't back off even if he wanted (for example, the debt probably paid not by their consent, and if they refuse to give their daughter, the collateral damage might be much much higher aka didn't give the family choice at all). Even if they let themselves poor, they probably can't live long anyway.
The vassals seems kind of... experimenting... 'how about force the duke to make heir in wolf form??' sacrificing innocent lady... kinda crazy I know =w= but I must applaud their loyalty coz usually in this kind of story the vassal betray the dukedom and gain their throne and lol 'the medicine to cross breed' HWY THE HELL YOU HAVE IT IN FIRST PLACE DEAR BARON no i dont think its your kink youre a very very loyal vassal arent ya may god forgive youuuuu