Ignore what anyone else thinks, it's about you and oh. He's your son and you are the ones who live with it day in day out. Dd2 would have been just Sam if a boy (but expecting a girl). Max is a lovely name. I would just avoid discussing it further with your family and announce him as max when he's born and your family will have to live with it.
I personally can't see that Giles is much more of a name than max, they both have one syllable, even if Giles has two more letters it doesn't take any longer to say!