What you didn't say...
Did your son have a written agreement about her paying him any of this for any of that ???
You also stated that "hers remains".... Did she walk off and leave it ? He is required to leave apartment in good condition or loose his deopsit and possibly pay for anything the apartment complex has to do to the apartment.This includes, him being responsible for the removal and disposal of anything left behind. Apartment complexs generally will store items left if of value and then to get them back you must pay them for all the work and storage for the items. I am not sure they are required to store anything, but end result, he ill be the one they come after. NOT her. He may be able to notify her that she needs to remove items <example>say within 5 days of his lease being up or he will have to move it.This allows him time to move it if she does not. Notice should be written.Have your son find out, if she didn't take it with her and does not get it, he may have a right to the items or at least the cost of packing,moving, and storage money...... Even if he stores it in his home, I THINK he can still charge her storage. This would help him recoup. Give her a time to come up with money for expenses... his time is worth money. If she does not fix issue in alloted time (also notice in writing of time frame and amount due by that time), he may be entitled to sell items. As this would mean she choose not to get the items back on her own.
You yourself, as stated should stay out of this if at all possible. And it is, I have a 19 y/o...... She is adult now. I do advise her to do the right thing beforehand and afterwards, I am always left out of the end result. But to bring in, your ownership to this matter. Don't do it.
Also is, do you have proof i.e. you got this in settlement, for if you did not walk away with it and courts did not award you it. It is more then likely hers. I had furniture, he gave up any rights to by not making it apart of divorce decree, although he was only one on the store account, still marital assests. He cannot come back now and claim any item I still have that was bought within the marriage. If it is legaly yours, I would have son let mom know that when you (dad) found out he had it in his possesion, that you came and picked it up because You (dad) have proof it is actually yours. You better have proof besides the store bill.
If he had no contract with her, I say tell your son to let it go, it is not worth the fight with his mom over. Also stated, courts are funny on how they handle family issues such as these because they are dumbfounded that the american families have sunk to this type of action.
My example.I lent money to my brother, several thousand dollars. Him and his wife were going to loose their home. I got the promise (words) they would pay me back as much as they could each pay period. My brother I did not trust but his wife I did totally. End result, they still lost the home and I never received a dime. I chose to walk away..... I am still on speaking terms with my brother and his wife.I choose this as more important then money. I also have a wonderful nephew that if I made issues over this may have never been able to see and now have a relationship with. (he was a minor then) I learned not to ever lend family money, if I can't do/give it as a gift. I say no.
Your son may be angry now.... is this worth loosing his relationship with his mom over ? You can support your son but also at the same time not get into this. Let him know you support him no matter what his choice is, but you cannot be and will not be brought in the middle of this. I think he will understand....
ANYTHING I STATED HERE IS OPINION, check it all out before acting on, no judge will rule in his favor because some lady in Virginia said this is the legal way to do it. I know this is how I had to handle a situation such as this and this is how I was legaly told to deal with it.