I've worked with FFLs dealing with estates in this manner in the past.

Ask them if they want to sell the guns or keep them, meaning don't allow them to price the guns out of market value and then get angry when the guns don't sell. I've seen estates pull their collections from FFLs because the guns weren't selling fast enough when the guns were listed for more than market value.

Make sure all parties are in absolute agreement as to the pricing prior to any sale being finalized. If you are getting a commission for helping out make sure that all parties are in full agreement on this as well. Make sure that all parties are aware that some guns will take longer to sell than others and set expectations accordingly.