It's not uncommon for parents to overpreen the babies. It happens in larger birds too. Sometimes it will go so far as to end up in mutilation and death ...they will preen off the ends of the wings and toes! So, its probably good that you pulled the chicks.
As far as the two chicks you talked about, I'd have to really see the behavior to know for sure what's going on. While it's possible that the older chick is feeding the younger one, I think that something else is happening..
They will solicit anything for food ...even each other.
If both solicit each other at the same time, they can both try to feed from each other. This can appear that one if feeding the other. I've seen this happen with other
baby birds. This seems more likely,
..but then again, I didn't see it, and don't know for sure.
You should continue feeding the birds. They sound like they are getting pretty old, I'd keep feeding them, but also start offering seeds or pellets to them so that they can start playing with it and preparing to eat on their own.
Following the suggestions of the breeder sounds like the right thing to do at this point.
Bob
