Is it normal that my little brothers flash me?

Ok so I'm 18 and my little brothers (twins 12) for some reason like to flash me a lot! I mean ever since I got on holiday break for Christmas it's been practically every day! I tell my parents and they say they are just excited to see me, but I don't think that's the only thing. And I was right because last night my mom and dad went to dinner and my brothers were taking off there clothes for no reason and started to wrestle! They were touching each other's little d**ks and practically laying on each other. I walked in and immediately stopped them. I was like "WHAT THE HELL ARE YOU DOING!!!" they said they were just wrestling. I was like why are you two naked and they said cause it feels good. I asked If mom knows about this, they said no, I asked if they've done this before and they said yes! I was soooo angry with them, but I calmed down and I told them to put their clothes on and not to do it again. I don't think they are gay, I think they are just both going through puberty and exploring each other. They both have some hair so is this normal?