Wild caught GBRs are very shy unless there are dither fish in the tank. A good dither fish is one that is a prey-type fish that is active and playful out in the open when there are no threats. Neons sadly are very reclusive (at least in my experience), making them pretty bad at this role. The GBRs are looking at the Neons, seeing them be hesitant & skittish, and therefore think there's something to be scared of.
Better fish for the role that fit your tank would be Rasboras, smaller Rainbowfish (Threadfins are my favorite), Guppies, Cherry Barbs, etc. These fish are fairly confident and active, which will signal to the GBRs that it's safe to come out. It's kind of like a "Hey, if those guys are out there being that dumb and not being eaten, it must be safe for me!" type thing.
Btw, are you trying to let the Rams pair up? 25g is perfect for an adult pair, but you may have territorial spats in such a small tank if you keep all 5 till adulthood. If you're planning on dropping back to the pair, you have plenty of room to add a school of small dither fish.
