If you can cope with the mortgage payments and do something about the arrears in agreement with the Halifax then my advice would be MOVE BACK IN QUICK! It sounds as though you have some money at stake here in the equity and it would be foolish to lose it and give yourself all manner of debt problems and credit stains when from what you say a solution is available.(posted 7990 days ago)If as I understand the mortgage is still in your name then it is you that have the cards in hand. As to the son you mention who seemingly is not helping progress matters, rather than sell out to him, once you have moved back in I would say you have a much better negotiating hand since he can't sell the property without your agreement (or a huge legal fight anyway). If I was in your shoes I would see about squaring things with the Halifax and applying for a re-mortgage with them or another lender in order to buy out the son's share. As you would be the occupant, you can offer less than the current equity value and if needs be play for time.
Above all though DON'T LET YOURSELF BE REPOSSESSED!