At present you don't have a right to sell the property - the executors of the owners' estate do.
That may well be you - but you have to establish your right first by applying to the probate office for Letters of Administration.
If you are in Scotland (the use of the term heritable property suggests you are) the words are slightly different but the principles are the same.
Halifax should be ablr to tell you if the mortgage was/is being paid - though maybe not by who.



