People around me are saying I am an AH but I need the perspective of uninvolved people.
My long term gf has my apartment keys, as I have hers. Only unspoken but always respected rule was, if you need to go to another place, just send a text “Hey going to your place”. Doesn’t matter if the other is at home or even responds. Just simply to tell the other you will be at their place.

I was supposed to be away 700km from home for 2 weeks for work related stuff, but 4 days in and our instructor got into an accident.

Work tried to find another one, but no such luck on very short notice. They decided at like 10pm to get us the 1st flight home the next day at like 6am, pay us the overtime and the next day at home, then resume our normal work schedule.
So I get home the next day at like 9am, sent a text to my gf to tell her I am back.
Getting to my door, I am very confused hearing children screaming inside since none of the people who have my keys have low kids like that (my brother and my gf).

I thought I got squatters or something. Opening the door and I see my gf’s sister’s kid running around after a shower, putting water everywhere. Plates of half finished ravioli on my living room ground. Their suitcases opened in the entrance.

I get inside and see the husband on my couch trying to hook up my PS2(that he must have digged out in my storage room). Getting into a verbal argument with him trying to understand why the fuck they are here. Said my gf told them they could get my flat for 2 weeks while I was gone (they wanted to visit the city for a bit, go to the beach). My gf sent me a text while i was arguing, telling me “oh ok, btw my sis fam’ is at your flat”.

I admit I blew up on him and the sis who left my bedroom in the meantime. Told them to leave immediately. They argued quite a bit, my gf called her sis, then sis put up the speaker so we could all hear, and she said I was embarrassing her, that she told them they could use my place for a while.

I threatened to call the police, also asked my brothers to come.
They left while cursing me to their children, telling that holidays are over because the mean little sister’s boyfriend cast us out.
I have now all of my gf family on my back, and even some of my own family, saying i could have stayed with at my gf so the kids could have some vacations…

Also. They have read my doctor prescription papers(I put them in a specific order, and it was not the same), and obviously took some of my prescribed meds (opened a box of benzodiazepine…).

AITAH for making them leave? We pretty much stopped talking about anything else with my gf. I feel like i am being gaslighted. I would never invite people to her apartment like that, especially without telling her. It seems so disrespectful.
Am I going insane?