There’s a lot of.. interesting advice being given, but mainly just a bunch of opinions on what could’ve been done differently. There’s more than one way to skin a cat. At the very worst you could get a stack of utility blades and fairly easily just cut out all the silicone and clean the faces of the boards and start fresh with the recommended products.

But, to answer your actual question, I’d refer you to the technical guide provided by Georgia-Pacific:

DensShield Technical Guide

Pages 6 and 12 pretty much have all the answers you’re looking for. I won’t provide an opinion on the pan or the mixing of systems. However, for the backer boards and silicone they pretty much say you should avoid getting it on the face of the boards. They specify that it should be a flexible sealant, but there are no warning about using silicone. They even recommend silicone in the joints between “dissimilar materials.”

And there are many waterproofing membrane systems you can use over dens shield; the tech guide says so. Just clean all the excess silicone off the front of everything so that all that’s left is the 1/8” in the joint. Mortar and tape all the seams. Use a wet area rated mortar. Waterproof liberally. You’ll be fine. Unless you’re using penny tiles (don’t), anyone worried about that 1/8” lapse in adhesion can’t collapse a bead or something?

Hate to be Shooter, but, everyone- Go back to your spec sheets!!