They can force a sale if you are either refusing to buy them out or have no reasonable prospect of raising the money to buy their share. They own part of the house and can enforce on that basis.
The fact that the house title deeds have not been changed would not be a problem because a buyer would simply need to know that you have the right to sell the house and the Will provides evidence of this. The house can either be transferred now at the Land Registry but equally you can wait to either buy them out and put it in your name and that of your husband then or if you do sell it can be registered by the buyer
I hope this helps. If there are any further points please reply