I want to stop paying my parents rent

I live at home with my Dad, Stepmum and their two kids. My mum died 5 years ago and my older sister got kicked out shortly after due to drug use in the house. I also work for them in the family business.

They’re constantly mentioning me moving out. My younger sister has already planned the layout of her room (my room) once I’ve moved out. My Stepmum sends me links on houses for sale. I honestly don’t feel welcome at home.

I pay them £300 rent a month - I get that paying them rent will help me budget for what it’s like living on my own but at the same time I can’t afford to save to move out. In total I’ve paid them £8,700 in rent which could have been my contribution to a deposit on a house with my boyfriend.

It so frustrating and upsetting knowing that I could be in a position to move out when I know for a fact that, that money is just sitting in their savings account doing nothing.

Is it rude of me to ask to stop paying rent?