Name question

Elizabeth

My sister in law is pregnant and having twin boys in July! I am shortly behind and due in September! My question is - one of the names they have picked out is Matthew. I am not sure if they will call him Matt or not...but, I really love for a boy (if it’s a boy) Max. That said, do you think the names are too similar? If so, any suggestions like Max? I’m a teacher so picking out names is about as hard as picking a needle out of a haystack.