ugh. wow so sorry you’re horses were so mistreated at that “trainers” house!
first, good for you for not locking them in a stall! If it were me, Make sure they have 24/7 hay available and wait it out. I would not do the collar thing. (UGH) to slow the horses down while eating use slow feed hay nets. Smartpak has some, and you can get other ones that fit round bales and small squares. they are a LIFESAVER for me! I would not be without them.