IPDI and existing mortgage

Hello, hoping you can help me with this one.

Husband has died leaving IPDI in his half share of property to wife, remainder man is their only son who also lives in the property with mum.

Problem subject to a mortgage which didn’t get paid off when husband died.

Lender requires the property to be in wife’s sole name so I have suggested lodging a form N restriction to evidence the IPDI. Wife and son happy to stay in the property so no concerns re making it more difficult to sell (these restrictions are then difficult to remove).

But wife tells me she and her son would like to remortage going forward which would mean property would have to be in joint names.

Proceeding with transfer to sole name with restriction will make it extremely difficult for her to do this.

Should we vary will to remove the IPDI so son inherits dad’s half share? That would facilitate a remortgage but could leave mum in a tricky position should they fall out and son wants to move on.

Also if we do this we will now need Probate presumably?

Could we do as above but then prepare a declaration of trust setting out the percentage shares but then give mum a life interest in that document?

Hoping you can help.

Deborah