Have you talked to your mother? Have you explained the disappointment that you’ve invested your time and money into this home and she hasn’t taken that into account? Are you absolutely positive that your brother hasn’t sent any money (I’m sure you are, but worth asking the question of your mother).
Tell her that if she’s going to split it 50/50 then you can’t put your money into it unless either your brother puts in the same amount or that you get IN WRITING that together you’ll keep an accounting and that will be reported to her lawyer or whomever on a monthly or quarterly basis and that amount is factored in to the inheritance. In short, if you put in $100, and the total inheritance is $1000 – then first you are made whole, you get your $100 back and share $900 or half of the cost is deducted from your brother’s half. You get $550 and he gets $450. It ends up the same in either direction.
Now, this doesn’t take into account interest or loans and it shouldn’t cover things like food or utilities. Those are normal living expenses and you’re living there. But if you move out and you want to pay mom’s heating bill – then it’s an expense on top of your other expenses. This would be for things like plumbers and a new roof. General maintenance to keep the place livable. Not furniture, not pillows, nothing like that. Those you should just keep receipts that prove you own those items so they aren’t lumped in with your mom’s assets.