I'm sorry for your loss, it must be an incredibly difficult time. I can understand how your initial reaction to someone asking for money that your mum left you would be to protect it at all costs. However, you're an adult and you need to pay your way. Your stepdad may own the house: but he/ he and your mum would have had to have worked their butts off to pay for the mortgage on it in the past, so regardless of whether he is workin or not/ owns the house or not, you should be contributing.
If your mum decided to support you, that's really lovely, but obviously your step dad feels differently, and it's not his responsibility to keep you rent free/ with free food/ electricity etc.
I can understand why you would want to keep hold of the money because she left that for you. However, if your stepdad decides that he wants you to move out, you'll be looking at (at the very least) outgoings of hundreds of pounds each month.
He's lost your mum too: it would be a shame if this money came between you, when you should be closer than ever, to support each other through this upsetting time.
It's understandable that you would want to spend on something which you think is fun, but you will earn money in the future to be able to do fun things. If you can't resolve this and end up moving out, you'll have to give up on your training and go into a part time/full time job to pay your way.
Money to do 'fun' things can be earnt anytime: but what's important is that you can support yourself and not have to rely on others to do it for you. You're your own responsibility and I don't think it's fair on him to expect a free time of it.