Standard visa for mother in law visiting - documents questio

[daugavpils]

Hi

I am a UK citizen and my wife is a non EU national on spouse visa. We would like to have her mother to visit us in July this year and I have some concerns about documentation that we need to provide to apply for a visa.
We have already bought a ticket for her as we could use airmiles and cover the cost of ticket with them.
I am fully employed and my wife is not working at the moment. Accomodation wise, we are renting and in the process of buying house. Unfortunately the house buying process has been dragging for a long time . Initially we were hoping to complete it in early May and use the mortgage agreement as a proof of accomodation.
We have already given the notice period to our letting agency for moving out in May, however they are flexible and are happy to cancel our notice and extend our stay till middle of June. My concern is that if even we do ask for a letter from letting agency , it still may mention that our stay in current flat until that date only, not July when mother visits.
The second issue is that I have changed my job three months ago and I can only attest ( get stamped) payslips for these there months. I do have electronic payslips from the previous employment but I won't be able to get them stampted as I don't work there anymore. This means that out of 6 payslips, only 3 will be stamped.

What are the possible ways to minimise the risk here? Could I book a hotel for mother in law and then cancel the booking? Surely she will stay with use whether the house purchase goes ahead fast enough or not.
And is my concern about stamped payslips valid?

Thank you!