What the hell is a DGG??
Your son needs to stop picking up after them.
Just stop.
He should tell them their rooms are theirs to sort, clean, tidy. Put clothes away, open windows to let in fresh air, the works.
If they want clean clothes and bedding etc, then they should see to it that their dirty laundry is put in the laundry basket.
When items are washed, dried and folded, then he can put piles on the stairs so they can pick up their pikes when they go past - there's no excuse not to!
They have a certain amount of time to have their tasks done by, or any filthy dishes & cutlery are thrown out (or hidden) and each person is reduced to one side plate, one dinner plate, one bowl, one cup/mug, and one set of cutlery. If they don't wash them, then they eat off dirty!!
If they don't sort their laundry, they go out dirty.
If they don't like going out dirty & smelly, then they should sort their laundry.
All phones etc to be taken away until they learn, except when needed for school/homework, which should be done at the table or in the lounge with no TV to distract them!
At their ages it's utterly disgusting that their parent has to run after them like this!!
What are they like at their mothers, if they go there?