We don’t have the key
Dong Xuelian did not doubt a word that came out of Master Liu's mouth. According to her, Master Liu was the only one who was strong enough to be kept as for the other three they were useless. Most probably that woman was also keeping these three ghosts as a supplement to refine some revitalizing pills or talismans but couldn't do it, so she ended up keeping them as a servant.
The more Dong Xuelian thought like this, the more convinced she became. Her confidence which was already searing through the roof became even more emboldened and she threw the talisman at Master Liu causing him to scream in pain as the talisman caused his entire ghostly form to be covered in fire.
"Are you going to tell me where the keys are?" Dong Xuelian questioned as she looked at the man in front of her. But Master Liu shook his head, he was not going to let this woman steal the treasures of his master much less hurt his family.