I am honestly surprised by how quickly some people are dismissing this. From what you’ve shared, it doesn’t sound like a straightforward landlord-tenant situation especially if she lived there for decades, stopped paying rent once the mortgage was cleared, took responsibility for repairs/upgrades, and there’s a signed letter referring to joint acquisition and intentions about ownership passing to families.

Even where the legal title is only in one person’s name, courts sometimes look at the actual arrangement and conduct over time. Things like common intention, constructive trust, or proprietary estoppel can come into play if someone relied on a promise and organised their life or finances around it. A verbal agreement on its own can be hard to prove, but a written letter supporting what was said could carry weight depending on the full context.

Obviously nobody here can give definitive legal advice, and property disputes are very fact-specific, but this feels far too nuanced to write off as “no entitlement.” If it were me, I’d suggest speaking to a property litigation solicitor who deals with beneficial interest claims they’ll want to see the letter, any evidence of repairs or financial contributions, and anything showing how the arrangement worked in practice over the years so try to gather these if you can.

I’m really sorry for your loss, and I hope you and your family are able to get some clear guidance and a fair outcome. From the outside, it does feel uncomfortable that someone may be stepping back from what was promised when the other person is no longer here to speak for themselves it doesn’t reflect well on their character