I was playing Bohnanza with some family, my brother-in-law kept trying to negotiate three-party trades. I felt like this was against the rules but as long as everyone's trades were planted at the end I let him get away with it.
E.g.
Mom, I'll give you a red bean if you give sis a soy bean. And sis you give me a garden bean.
Is this against the rules? Should I have stopped him?