Your fears are valid, but in the end of the day it's what you want and your future and you have a clear idea of what you want to achieve. Personally I always expect the worst it means I can mentally prepare for any outcome, though I do hope that isn't the case for you. I would sit them down and tell them matter of fact "this is what is going to happen, this is what I expect to change and what that means going forward for me" but I know that can be hard to do.

As you say you're in a situation where they can use your housing situation against you and it could go that route if they've done it in the past, so prepare for that. I would make it clear that this is going to happen without their consent, you are an adult, you can make your own choices and have lived socially as a trans person for 4 years, it isn't going to stop. (just so they know it's not a phase or some ignorant shit y'know) You need to be assertive and I know that's the hard part, I know it could upset the apple cart but again it's your happiness and future.

I know this isn't easy in the slightest, take as much time as you need to prepare and wait for the right time, I hope they'll co-operate with you