<human>: Could you distill the essence of the text into 1-3 sentences?

So I'm currently living with my mum and her girlfriend. We live in the UK in a three bedroom council rented property. 
When I finished school, I was pestered into getting a job. My mum said I should so that I could go out and do new things before I start having to work (I had guaranteed an Apprenticeship with an Electronics company at the end of the summer holidays), whereas her partner said I should so I can start paying them rent. I don't get on with her at all, and haven't done for the entirety of their 12+ years of relationship.
I replied with something along the lines of "this is my last proper holiday before I work for the rest of my life: I want to enjoy it. Besides, you can have fun without money" each time they ask me. 

As soon as I start working, I pay rent. I also have to pay for my own food. I don't mind that, but on an apprenticeship wage of 700 pounds a month, and paying them 150 pounds rent, it was a stretch: At the time I was paying for my car monthly, and paying for my driving lessons (they had said they'd pay for them like they had done her partner's daughters previously, but then suddenly changed their mind and paid for my license instead), so I had perhaps 80 pound for food a month. 

Fast forward a year, and I'm now on 1004 pounds a month, paying for my insurance, paying rent, and paying to keep my car on the road. No problem. I'm now 18, and I'm looking to find a place of my own with some friends. 
The problem is however, that my stepmum's daughter now also has an apprenticeship, and as far as I'm concerned, doesn't pay rent or have to buy her own food. 

I want to know if there is some sort of legislation that states I actually have to pay rent, as I'm still actually in full time education being in an apprenticeship, and I study at a college one day a week too?
Or are my parents taking my money simply because?
<bot>: Are my parents making me pay rent because they don't like me, as another member of the household doesn't seem to be paying rent, or am I legally obliged to?