Losing War

I’m making a Battania only playthrough, they decided to declare war on 3 other kingdoms and we’re losing most of the major battles, lords (me included) keep getting captured, losing castles and I don’t know how to help. My clan is only a tier 2 one so I can gather bit over 100 troops which aren’t much help. Is there a way I can influence a peace treaty if I’m just a vassal?