well I am about to tell you what you need to hear not what you want to hear.
but first i will say, i am sorry for the situation you are in , and i truly hope the issue with your boys will be worked out.
Have faith that in thier manhood (whatever age that is when they achieve it) will want answers and the truth of it all.
I recomend that you keep some sort of records,aka the returned letters and such, as there is the posibility they do not even know of your attempts.
Now as far as thier room... I am a home specialist, For a living, and i can tell you 1 thing for a fact.
If you have not been in that room for a year and a half and there is anything growing in it you have bigger problems than you think.
there is moisture in that room, or there is no airflow to remove the combined moisture.
I hope the problem is easily fixed
without even asking i assume the door has been shut and, also without asking i can assume that the crack between the door and the floor is less than 1 1/2 inches. I hope if not you have bigger problems.
I see this problem on about 40% of my calls for moldy walls, closets and the likes.
when the door is shut air cant flow through the room, the average air vent in a room is 40 square inches inflow but if the door is shut and no 1 1/2 crack the outflow is restricted or as much as stopped on rooms where the door touches the carpet.
if this is the case keep the door open or have friend cut off the door for you ( if its a hollow door the bottom binding will be cut off with it and require glue and clamps to restore it) private message me for more details on the fix of the mold problem
as JUST cleaning the room will not solve it if that i all thats done, a room in a properly maintained home should be able to have the door closed indefinitly, without worry of mold, as mold is not a sign of dirtyness or cleanliness, but of moisture.
as far as the problem as it is, i understand your reluctance to enter it, i truly feel bad for you. I highly recommend you ask a friend to do it for you. seriously, a true friend will understand, the entire room needs cleaned up, what is trash trash, what can be washed needs washed, and then it can be decided what to do with thier personals. I also recommend The 3m P-100 resperator mask from lowes, the P 100 is good for mold spores, which CAN cause LUNG INFECTIONS in humans. THIS PROBLEM IS SERIOUS TO YOUR HEALTH, aka prolonged sinus problems at the least. pm me i will try to help all i can with knowledge. NOTHING HAS TO BE thrown away i can tell you how to safely clean everything to non hazardous state
be strong on the mental side, time has a funny way of working things out.