A couple concerns from what you posted above, have arisen with in me. Don't take it personal, but I'm about to point them out to you.
First off, You need to separate them. Not just because THEY
CAN AND
WILL MATE, but for health and safety issues. Unless you see it yourself, you don't know which one defecates, so how do you know they are both passing OK? If one has an underlying ailment, then it won't be long before the other one has it too. Just ain't good to house two snakes together unless, first, you know both snakes to be of good health, and, you are trying to breed them.
It's been recommended by everyone to go see a vet. You're putting the animals health at risk by not doing so, and trying to pick up something from the feed store to treat it with.

That just ain't cool with Me. The animal deserves a vet visit, or someone else who will.
I fed live for many years, until I found out people started feeding F/T. So I tried it, and even the ones who had only had live their whole life switched with only a little effort on my part. So i don't buy they won't do it.
If they don't eat it, make them wait until their next scheduled feeding, and try again. Not in a couple days, but a full week at least. Try leaving it in the viv at night for them to find when all is quiet. (dead of course) No wait, you can't do that because you housed them together.

But if you housed them separately like a responsible owner, you could.

There are tricks to switching, it's been proven time and again that they WILL switch.
My humble opinion
Rick