A weird friend problem help?

Ok so im friends with these girls, lets call them May and Mary. Ok here's the thing, they are twin sisters. Now I like having Mary over because May is really whiny and always wants to do what she wants and shes always loud when my parents are sleeping. So today was my first time having Mary sleep over. I was a bit scared but she never whined and she did like a fair share. She was loud when my parents were sleeping but it was an accident because she stubbed her toe -_- lol. So I like having her over more now. Except now May is mad because she thinks that she can't come over anymore. I get what shes saying, but it's kind of true. Like they are really good friends and you can't have them both over at the same time, trust me -_- lol. So what do I do?