As a single person you'll get either one bedroom or shared home rate for local housing allowance. So first step is to find out what amount that is for your area. There's a webpage for it. As you're working you won't necessarily get the full amount.
Next go on spare room.com and check out the average cost of a room to rent.
Then go on entitled to website and enter your hypothetical future details as if you'd already moved out into one of these rooms. It will tell you what benefits you may get and is fairly accurate.
Do the same thing for a one bedroom flat. So you can see how it compares.
Whilst it's nice to train for a career, education past state age isn't a right it's a luxury. If you can't afford to move out on your apprentice wage, consider whether giving up your job and taking a minimum wage job somewhere else is the right option. Even if you choose to remain in this exploitative situation living at home until you've qualified and earning more, knowing you're choosing it gives you back control. Many people can't do a job of their choosing because they can't afford time out from earning a proper wage to train. They need to do a job that pays the bills. You're in charge of your own destiny OP.
In addition to whatever she's lost in other benefits, your mum will have lost 25% discount on council tax which is applicable when there's only one adult in the house. Council tax can be expensive depending on size of property and where you live.
I suggest stopping spending on your siblings and starting a savings fund for when you move out. You might need things like driving lessons, a car, furniture, rental deposit, hiring removals van. It all adds up. You need to start putting yourself first and that includes building a support network, which your family isn't suitable, so you need to spend time socialising with friends.
If your mum tells you to get out ensure you tell the council you're homeless, even if you're still there. The benchmark is whether you have a right to stay (you don't) and are welcome to stay if no rights (obviously not if she's told you to get out). If she does that don't give her any more money, you'll need that most recent months wages to pay your rent, benefits are paid in arrears but rent is paid upfront. If you have a prepayment meter for gas and electric that's paid upfront too.