All this talk of "it's not faaaiiirrrr" makes posters sound like they are about 6! As though the brother got more sweets or pocket money or something! You are all adults FFS! and the OP should love her brother enough that she is happy for him that his home will be protected after the death of his mother.
I now feel very fortunate that my brother and I haven't spoken about 'favouritsm' by our parents since we were in primary school. I had no idea that some adults out there are this petty!! I think my parents try to be fair, but being fair doesn't always mean giving the exact same thing to everyone.
For example my parents paid a lot of money for my brother to go to a special boarding school because they felt it met his needs better than any other school. They didn't pay for me to go as they felt a different school met my needs better. That is still being fair, despite the fact it meant they spent about £50,000 more on my brother than on me when we were growing up. They just wanted what was best for him. Should I now be banging on their door asking for my share?! Of course bloody not! I love my brother and am glad my parents were able to help him out in the way they thought best.
I've noticed over the past few years that despite being financially comfortable my parents dont really spend much money. I mentioned this to my dad recently and he said that they didn't want to spend all their money so there was nothing left for my brother and I. It nearly broke my heart to hear him say that as I have never even thought about getting my parents' money when they die. In fact I genuinely hope they don't leave anything as they live a long, happy life having as much fun as possible.
If I heard now that they planned to leave their house to my brother and nothing to me, I would find it strange but would be happy for my brother as he earns less than me, and would bear no resentment against my parents as the money was never mine anyway so it's not like I would have lost anything anyway! Only a child would think 'that's not fair, they must not love me' - like I used to think if my brother was allowed to watch a tv programme that I wasn't allowed to! In the OP's situation it's not even strange as the mum is just making sure the brother keeps his home!
I think you need to grow up, stop thinking like a child and realise that there's far more important things in life than who gets more money than who!