My wife's mother deeded her house to my wife and her grandson before her death. Now about 3 months after grandmother's death the grandson has demanded that sale of the house proceed or he will petition the court. My wife reluctantly agreed as she originally wanted to fix things wrong and rent the house and split proceeds with the nephew. The nephew is executor and has exhausted assets of the estate except for furniture etc. And is now attempting to get my wife to pay utilities and insurance. Can the nephew force my wife to pay utilities?

I have one more question related to my first question "Co-ownership". When and if a buyer offers to but the house does my wife have to accept that offer? Also how many subsequent offers can my wife turn down?

She can keep turning down all offers but then the other person can petition the court to force her to sell.

I will assume she can not buy out his share, perhaps get a loan for 1/2 of the value

It depends on what he did to exhaust the assets of the estate. If they were exhausted in paying off the debts of the estate then yes he can ask your wife to help pay those costs pending sale of the property.

If he has to lay out money to pay the expenses, he can recover that money from the sale.

It depends on what he did to exhaust the assets of the estate. If they were exhausted in paying off the debts of the estate then yes he can ask your wife to help pay those costs pending sale of the property.
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I don't see what the estate has to do with it. As executor he could not, in any event, use assets of the estate to pay expenses of a house he owns in common with OP's wife.

I don't see what the estate has to do with it. As executor he could not, in any event, use assets of the estate to pay expenses of a house he owns in common with OP's wife.

I'm assuming here that probating the estate has not been completed. Based on what has been said, I don't think it has. But if it has and ownership of the property has been transferred, then one owner can ask the other owner to share in the expenses.