If the house is repossessed by a lender they sell the property under a special power of sale so use a different transfer document than is used in a normal sale (a TR2 rather than a TR1) and it is signed by the lender who repossesses (sometimes by the solicitors who act for them under a power of attorney) not the people who own the property.
The special power of sale also means that it overrides other charges which normal sales cannot do unless they are paid off. They can sell even if the property is in negative equity (more owed on the property than what it can be sold for).
As regards money back, it depends what is left as people often owe far more than they realise, especially in repossession cases due to early repayment penalties, arrears charges and solicitors fees once the account goes into litigation. Then there are the costs of the sale itself.
It also depends on how much they get for the property as it's not a great market at the moment. Many are sold at auction and due to the limitations on finance and people having deposits it's pretty much down to cash rich investors or those who have a deposit and can get a decent mortgage.
Even though they can override other charges on the property, anyone else with a debt secured over the property would be paid off from any monies left before any monies were returned so you should check if there are any other charges secured on the property, charging orders etc...
As to entitlement to money, it is not that clear cut, it depends on your respective interests and agreement. Get some legal advice as regards the money aspect.