AITA for refusing to let my mom and brother live with me in a studio?

I (26f) live in a major city of a second world country. My mother bought me a studio apartment as a graduation gift. I appreciate it and I know not everyone has the same privilege in life. It was bare finish (or rough finish idk, there was nothing only concrete walls).

The apt is in my mother’s name but I never thought much about it until a few months ago.

My family (mother 56F, stepfather 60M and half brother 16M) live in a small town in the same country.

I was told by my mother that my halfbrother (same mother, different fathers) wants to move here and attend school as the school he’s currently attending is not good and he would live with me. I said that it is completely unacceptable, as he is a minor and the apartment is a studio (300 sqft). I told her that i am not his parent, so why I should hold this responsibility?

She answered that family should help family. I said that it doesn’t work like that and If my brother wants to move to a big city, he needs to get good grades, do good in a high school final exams, get accepted to college and move into a dorm. Anyway we had a big fight and didn’t talk for like a month or so.

Today she called me and said that they would move in anyway. She thinks that because of my remote work I don’t need to live in this city, and out of her two children my brother now needs it way more. My mother also said that she isn’t kicking me out, I can stay here or I can go wherever or I can go back home.

Well I can’t go back home as I won’t be living with my stepdad cause it would be really weird. I can’t stay here as well because it is STUDIO. So basically she is kicking me out right?

I literally begged her not to do it, as this apt is my home. It is a tiny shoe box, but it is mine. I made all the renovations how I liked, decorated, bought and assembled the furniture by myself.

At the end, I suggested that they rent another apt in my city for 2 years (while the brother is still in high school) and I will pay for it if she legally transfer the ownership of this apartment to me. She doesn’t like this idea because there is a saying “even though the place is crowded, we don’t mind”.

I just feel so betrayed,I cried the whole weekend. If she would’ve told me beforehand that it is not mine, I would’ve used the money I spent on it as a downpayment for my own property.

I tried to reason with mom to no avail. I honestly don’t know if AITA?