It's actually not a good idea to feed in another cage...your snake is more apt to bite you while in feed mode, either before or after. With larger snakes it's actually
dangerous to do it that way, as some stay pumped up ("feed mode") for even a day or more after eating, so you can get bit trying to put them back in their cage.
The best way to avoid bites is to signal your snake that it's NOT feeding time, using your scent & touch (with hook or similar item). Some snakes actually will not
eat if you handle them first (just to move to another cage), it stresses them & interferes with their instincts to eat (because the only thing that normally picks up a
snake in the wild is a predator about to eat them!) I'm glad yours eat anyway, but it's not the best method, especially since you're getting bit.
As for them ingesting substrate, just feed on a "plate" (either a real paper plate or a cardboard box lid, or similar thing to keep the rat off the cage floor).
Sometimes snakes may be inclined to bite when they aren't being fed enough...without seeing your snakes & the size of prey, I can't tell if that may also be a factor.
There may be other issues going on too.