Have you signed a tenancy agreement?
Please explain in more detail, are you still in the property, has the other person moved in, what type of tenancy agreement did you sign?
The problem your grandson has is the agreement is verbal. His word against the landlord's. Without a written agreement there is very little that you grandson can do, sadly.
You are entitled to you belongings back. It would become a question of potential theft if the landlord refused.
Recovering any costs for the carpet and decorating will be difficult as you have no written agreement. Difficult to prove the terms.