If the house was formally a Principal Private Residence then a bank would have to obtain a Repossession Order to take possession of it, as technically the house is still subject to MARP. If the joint owner emigrated on economic grounds to obtain a job, his house is still his PPR under MARP provided it is the only property he owns in the country.
The approach of the vulture fund will depend on which vulture fund it is. Some funds will just "bulldoze" ahead and appoint a Receiver and sell the house in the hope that they get away with it. Other funds will be more cautious and go down the proper Repossession route.
If the house is in significant negative equity then the owners should consider a PIA, under which the mortgage could be written down to market value.
Jim Stafford