Don’t, please just don’t do this. You’re just opening up the door to her and are going to make her think that if she and/or aunt continue to apply pressure you’re going to cave. You’ll also be dragging your brother into it and you shouldn’t, your mum should have.
Plus what if he actually says he will give her money, be it 10-20 or even the 50k? You’re going to leave yourself in a dreadful position and all because you didn’t just laugh and say no.
I honestly don’t understand why you’re struggling so much with this, why are you trying so hard to please her at your detriment? She’s your mother, so what? What she is trying to do to you is disgusting, why can’t you see that? Everyone is desperately trying to tell you!
I wouldn’t give a flying fuck whether my mum spoke to me again if she had ever tried to pull something like this with me. No caring, loving, decent parent gives their child a gift, watches them buy a home, then asks them to sell their house because they have decided they want it back.
Tough shit. If she spent the 100k and cannot afford to buy a house in the area she wants then it sucks for her, not your problem.