L.C.
Crazy as this sounds, what if they slept together. If they both have separation anxiety and they both need someone with them to fall asleep then maybe they could rely on each other. My older boys were both the same age difference as yours and they both seemed to sleep more peacefully when they were together. Not only did they go down easier because they weren't alone, but they would sleep better at night because they would wake up and weren't alone.
Another thing you might consider is switching up locations where they sleep. We would start our kids out in the living room on the sofa, one at one end and one at the other. Or we would let them have a pallet on the floor. They seemed to fight it less when there was less of a production. Whatever got them to lay down peacefully. We put them in their jammies and just laid them down. Baths waited until morning or early afternoon. We had to eventually pick our battles and where they slept became significantly less important than how well they sleep.
Hope this helps,
L.