Tenant Deceased

Possession - Section 8 and Section 21

My Tenant recently died. The AST was just in her name and the fixed term had ended.
Her son asked for time to sort her affairs and belongings – and although we were not being paid any rent for this we tried to be as sensitive as possible.

It has now been a month and when I contacted him this morning, the son now says that he wants more time to empty the house.
[The neighbour tells me he is slowly selling items on ebay, so no idea how long this will take!]
He has also advised that he thinks he wants to move in to this house.

1. How to I get possession?
2. If the son moves into house does this affect getting possession in anyway?
3. If the son claims that he moved in before his mum died would this be in any different?

Looking forward to any assistance in this strange situation.