Cousin WAY overstepping boundaries

My brother lives in a different state. He is currently staying with my cousin (who is 31 and still lives with her parents) because she bought him a plane ticket for his birthday so he could come visit and look around the school he wants to transfer to in the fall. I should also add she didn't tell me he was coming because she had told him I knew the date he was coming but told her I didn't want to see him?! TOTAL LIE. The cousin in question and I used to be extremely close. I moved from out of state to go to college and I lived with her and her family. When I got a boyfriend (my now husband) in college she freaked and said I needed to break up with him or she was done with me even though the rest of the family liked him. Obviously I didn't break up with him and we're now married with two toddlers so my cousin and I have had an extremely rocky relationship since then (6 years ago). I now live 3 hours away and she has tried to replace the friendship she had with me with my brother who is 19 so considerably younger than her. So, my brother wants to visit me but my husband and I are sharing a truck right now because my car is in the shop until next week and because he works all day until 5pm, getting there is difficult. My husband is an amazing guy, treats me and our two kids amazingly and is always nice to my family. My cousin is insisting that if she drives my brother up to my house that I have to tell my husband to leave the house and go somewhere else so she doesn't have to be around him. Even though my brother loves my husband! My cousin dislikes him because we're happily married and have two kids together and she's still 5 years older than me, single, no kids and loving with her parents. She also says that if I drive down to her house and pick my brother up she won't let him leave if my husband is with me in the car and that he can't see my brother even though he really wants to. I have no idea what to do or say. My brother is going along with what she says because he doesn't want to get kicked out of the house because she lives 5 minutes away from the school he wants to transfer to in the fall and he wants to stay in his her good books. This is ridiculous right?! My brother says she constantly brings up to him how much she hates my husband and tries to get him to hate my husband too. What do I do here?! I don't want to tell my brother he can't see his brother in law because he really wants to see his face when he opens the Christmas gift he got him. What would you do??