Whenever we get new glider and put them on HPW with fruits and veggies (we just got 4 more and the same thing happened) they will eat the HPW but leave the fruits and veggies alone. the 4 ones just started eating some of the fruits and veggies and we have had them a few weeks or more.
for introductions I would continue with cages 6 inches apart and swapping stuff every few days for awhile, then put all three together in bathtub.
when we went from 7 to 10 gliders the 7 would not accept sweet pea, just 2 of them. so we had to keep sweet pea separate, we ended up rehoming her to someone that had one and they introduced their one with sweet pea.