What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
Buying a property with another party - Duchess
When Harry took out the mortgage, didn't the mortgage company require details of the other interests in the property (other owners or adults over the age of 18 living in, but not owning, the property)? Usually this is to obtain an indemnity that the mortgage takes priority over the other interests.

Speculatively, Jack can't be forced to pay Harry's mortgage but he risks finding the property sold against his will (court order required).

Had he taken out his own mortgage, it would be even more complex as only one mortgage would be the first charge - not sure if they would have found two mortgage companies to agree to this!)