If it's now a rolling tenancy, then there's no signing of new annual contracts
You can't just remove one person from a joint tenancy. If someone leaves, the whole tenancy is automatically ended, and anyone who wants to stay in the property has to agree a new tenancy with the landlord. Which is probably why uncle is hanging this out ... would he and his wife meet the income requirements by themselves now? If not, they'll have to leave.
I don't understand why you are so resistant to getting land registry details. It might not be the landlords current address, but it probably is. All you'll lose is £7 if it isn't.
And yeah, your mother was involved in scamming the landlord at the start of this, not sure why you think she wasn't.