Mortgage extension with multiple ASTs

Other

Hi there, just wondered whether you'd come across this before. I tried to extend my mortgage with the bank and they've declined on the basis that I have two Assured Shorthold Tenancy Agreements set up on the one property. Naturally the two tenants are reluctant to enter into a shared agreement. Both agreements are with young professionals and both have been in place for over two years.
The extension would have taken my total borrowing to about 50% of the value of the property and increased my monthly payments by 100 pounds so it's not an issue with the level of debt - just an issue with risk according to the bank.
Was hoping that you may have come across something similar and could suggest strategies to counter.