no, it's not yours, if you didn't pay it off there's a lien on the property to the mortgage company.
No.
Property in England and Wales has to be registered with the Land Registry. Once it is, the pile of documents known as "the deeds" become superfluous. It's likely that the house was registered when you bought it and that is why you have the deeds. You could give them to the person who now lives in the house or you could throw them away. You can check with the Land Registry website (for a fee) whose name is on the Land Registry Certificate, but even that doesn't necessarily prove who owns the property.