I am sorry you are stuck with this disease. I too suggest not adding any birds until all of your current ones die.Yes, we had a neocropsy done and it was confirmed to be Mareks. Our birds have all had very different symptoms so very hard to tell but I figure if one had it they all will.
If you must add new birds adding vaccinated for Marek's birds may help future birds not suffer as much.
Whatever you do for sure don't ever give away, sell or rehome a bird.