There appear to be a couple of different issues here that are all intertwined.
"I can't get him off due to financial difficulties so I'm stuck with it."
I think this is your biggest problem. I take it that you mean that you notified your lender and they came back and said that you do not meet the affordability criteria by yourself?
Or perhaps you applied for a mortgage by yourself and were turned down?
If that's the case then I don't think that you have much choice other than to sell.
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"BUT I have to get his permission on the estate agents I use, the amount I put the house on the market for and what I accept."
This sounds very confusing indeed. Was this part of the final order?
If so, is there some sort of wording that says something like "such permission (or consent) not to be unreasonably withheld" ?
What this means is that he has to act reasonably.
"...and has told me already he won't accept the highest offer"
OK, so it sounds like you need to go back to court and get an 'Order for Sale' from the court. This will allow you to sell the property without him making all these unreasonable demands.
Frankly, I would concentrate more on getting this done and then worry about the will later (unless there is some reason why you might want to have a will in the very near future).