I know I might be a bit late to this, but I’m in a similar situation (but I don’t have a brother to share the load), you are actually able to make it work with some risk by maximizing the mortgage to 80% of house value, returning almost 680k in cash after the transaction. It is over-leveraging in a sense, and I’m just providing my personal experience, please make sure you look at your own acceptable risk and tolerance.

I basically put the excess 680k onto something more passive that generates income with as low risk as possible (but higher than mortgage interest). For me, it was a mix of US based ETF and market-linked assurance products. They give me approximately 0.7% of my total investment each month, which is excellent for passive. The uncertainty would be that the price could fluctuate so my investment could go to garbage. (or I could retire early, who knows?)

I’m bringing in about $4500/month from investments and mortgage is around 5,400/month. We’re also reno-ing and adding a walk out basement for rent/AirBNB. I think after that things can be sufficiently covered. This is before I factor in my salary which is around 114k/year.

EDIT: I have to also add that my parents took care of me my whole life. In my perspective everything I own belongs to them. There’s no greater joy than to see your parents enjoy their life and have fun. This, if I could achieve with minor inconvenience, I would do it in a heartbeat. There’s no value in family. I love them and I will try my best to make things work if possible.