Thanks for that my research was inconclusive.

I need clarification on what type of tenancy agreement my son will need. He will be sharing a 3 bedroom house with two others. They will each have their own room but will share the use of bathroom/kitchen/living room. The house consists of a ground floor and an upstairs. Is it legal for the landlord to issue three separate agreements or should there be an AST for the main tenant plus two sub-tenants?