AITA for telling my fiancee that if her brother lets himself into our house again im changing the locks

Me (29m) and my fiancée (27f) dated two years and got engaged four months ago. She moved into my place after the engagement, i pay the mortgage while she covers utilities and groceries, and the plan is to put her on the deed once were married so she builds equity too. Her younger brother (23) is around constantly and hes polite enough to my face, but i never once agreed to him basically living here. The thing is he treats my house like his second home. He lets himself in during the day to do his washing, eats whatever is in the fridge including the meals i prep for work, and crashes on my sofa for three or four nights at a stretch without anyone asking me, then leaves the place a tip. When i brought it up with my fiancée she said hes just close with her and itll settle down once hes more sorted, which has been the line for months now. Then a couple of weeks ago i came home early and there were two lads i didnt know in my living room playing my console while the brother made them food in my kitchen. Turned out hed told them to come round because "no ones usually in during the day." I was fuming and told my fiancée i wasnt comfortable with him having that kind of run of the place, and she sort of agreed and then did nothing. The final straw was last week when i found out hed got the spare key id given my fiancée for emergencies copied and handed it to one of those mates so they could "use the wifi and the xbox" while he was at work. A stranger had a key to my house. I sat my fiancée down and told her flat out that if her brother lets himself in again without me knowing im changing the locks and hes not getting a new one, no discussion. AITA?