Another point is - what can the bank actually do if OP's father fails to pay the mortgage in full, provided he pays all interest and some (if fact, most) of the capital repayments?
While it is understandable that the bank does and will continue to pressure him for the full payments and will add extra charges if he falls in arrears and will also damage his credit rating, can the bank actually repossess any of the properties? Considering that OP's father is doing his best to pay and will in fact be able to repay in full, just a couple of years later than the bank would like.
In these circumstances would the bank really go to court seeking to repossess the properties? And would the court grant the repossession, considering the short length of time left before the mortgage will be paid anyway, the efforts made to repay and the very low LTV?
Maybe the bank is just bullying OP's father, pressuring him into selling at the wrong time, as due to low LTV the bank will still get its mortgage repaid anyway, even if properties are sold at a big loss?