UK Landlord Forum / Life

I have a grandmother, her daughter and her daughters son moving in soon. Only the grandmother and daughter are named on the tenancy agreement but the son is over 18. Does NOT being on the tenancy agreement mean he would have no right to stay if the other two move out? Or could he make a case to stay because he has lived there for 6 months etc?

It depends is it a council property or private landlord?