My dog looks depressed and i'm worried.?

my parents and i went to peru for vacation from july 1-25. and my dog stayed with my older brother. he's 19. it was obvious that my brother brought over his friends like almost everyday and probably went out a lot. my brother plays soccer almost everyday and he plays late, so since we weren't here my dog stayed home alone. my brother says that he didn't go over to his friends house, instead brought over his friends because he didn't want to leave snoopy alone. but either way i feel that he was still neglecting my dog while all his friends were over. and im scared that his friends might have done something to my dog. my dog isn't the same. he seems scared of people. and he's not active. my dad played with my dog a lot, like roughhousing and stuff, and my dog always played along and was happy. but now whenever my dad wants to play with my dog snoopy just walks away. and we also played with him, like making him dance. even though my dog was probably annoyed or something he never complained or whined. but now when we make him stand up on his back legs and we grab him by his arms he cries. or whines as if it hurt him. and my brother called us in peru to tell us that once my dog accidentally ran into the guitar hero drum set and started crying and lifting up his paw. then my brother said that he stopped after a while. every time i want to hug my dog or play with him he yells as if i'm doing something harmful, when i barley even touch him. im really worried that something might have happened to my dog while we were gone, that not even my brother knew about. my parents were thinking of taking my dog to the vet to see if they can do something, but i need some advice on what i can do before we do decide to take him. i just feel that maybe my dog is depressed. but then all the crying makes me think that maybe something else is wrong. if this has happened to someones dog please help, i'd like to know what you did for your dog to help them be better. i know this is a lot but please help. thank you.