Sister Brings Boyfriend to Family Home Without Notice

Per my last post here, this quandary is owing to my unusual living situation: I rent my childhood home from my mother, who lives in her second home elsewhere. I make a pretty small wage in an extremely expensive city, so while I would like to just have my own place, it’s not going to be feasible for a long time (my current company is even on a pay freeze).

My sister makes substantially more than me but lives in a busy house share the other side of the city. Her bf lives in essentially poor student accommodation in a different city. She’s recently been saying that she feels she’s outgrowing her house share, and that she and her partner find it really stressful staying there because of how busy it is, and they can’t get much peace together.

All that to say that last weekend they came to stay here in the family home, and then added two additional nights onto the stay without letting me know because they were enjoying the space. Now I’ve just had five hours’ notice that they’ve decided they’ll be staying here again, because the bf ‘really got stressed at the idea of staying in her house share’.

I basically said that I’m not okay with having such short notice, and I’m also not really happy if they’re trying to make this a regular thing: this isn’t an alternate place to stay for me, this is my only home, and I don’t appreciate a couple showing up whenever they want to get some space, and in doing so taking mine. My sister is angry because she says it’s her childhood home too and I’m not the one to say when she can or can’t come and who she brings.

And of course my mum wants to stay out of it lol.

So tl;dr AITA for trying to stipulate when my sister can or can’t bring her bf to stay in the family home that I rent on an individual basis. Mouthful.

EDIT: some info

1. I’m not objecting to them staying at all. Last week they were going to a game nearby so it felt like it would’ve been unreasonable to complain. I’m complaining about showing up at short notice, for indefinite periods, and regularly in a house that’s my full-time residence
2. I don’t pay market rate – me and my mum agreed an amount based on a suitable proportion of my income, and I regularly check in in case she wants increases. She’s currently happy with what I’m currently paying.
3. My mum sort of takes my side – in that she says she wouldn’t want them coming by as they do in my position – but won’t lay down the law personally because she doesn’t want to alienate my sister.
4. There is an official written agreement stipulating me as a tenant and my mum as the landlord.