You know, just because your husband wants you to do these meals - you really don't have to. DH can even make you the bad guy. He can call up BIL and say, "Actually, sorry we got our wires crossed and Susan actually has a prior commitment that day and won't be able to cook dinner. Looks like we can go out just the two of us." And if you DON'T have something going on that day - schedule something. A dinner out with girl friends, a massage, a book club meeting, a new exercise class, whatever. BIL acts dominant because you and DH allow him to be dominant by giving in and not saying no.
My husband is similar in the he never wants to go and see his parents by himself. Even though they drive me a bit crazy, the truth is that he just doesn't like spending time with them alone because I provide a good buffer or distraction. My in-laws live a good 5 hours away, so it's not very often. But it sounds like you see your BIL more, and you have much more to be fed up with.
Your husband is asking you for a favor - but you don't have to say yes. You didn't commit to it, so you have no commitment to honor. BIL sounds like a nasty creep, and you have no obligation to him.