Newbie here! Asking advice on sexual maturity of baby boars,please!

My daughter brought home her "baby" Donut, as a gift from her grandparents. Within a few days of having her, I had a feeling she wasn't just jelly-filled! After i told my Mother in law who said she had no idea, they were told they only sold females, I called the pet store to get the response that it happens sometimes but we could "trade her in"....i said a few choice things & ended the conversation...until this point I was completely ignorant about just how terrible these pet stores were!
Fast-forward and we now have Momma Donut, her two boys Snickers, Reese Cup & little girl Cookie. All healthy & very much loved! But my question is, is there any chance of the boys being sexually mature if they won't be 3 weeks until Friday? Tonight my daughter had Donut out for some lap time & just happened to look and notice One persistently trying to mount the girl.. I took her out and he started fighting with his brother.. I'm not sure if he's just practicing, but to be safe I now have the boys in one cage and the girls in another ( I had to move out of the room because he was trying to get to them !