They need to contact the council and citizens advice as well. The council need to know that they are at risk of homelessness
What is the FIL planning to do with his council flat? Is he handing it back to the council or planning to keep it illegally? The council could come and evict them if the named tenant has moved out
Do they have enough money to rent privately?
Estranged Son and Future Granddaughter
To think that London, or anywhere else for that matter, does not belong to any one demographic