Your instincts are very good, and I'm glad to hear that. You are right on target about switching to f/t, not trying to soon or too often to avoid stressing them, and separating them as soon as you can. Often it takes a little work to switch over to f/t and what works for many of us to begin with is to thaw the mouse to normal body temp (same as humans) or just a bit above, then "dance" it with tongs or hemostats gripping the back of the mouse, and if/when it strikes, tug back just a little bit to simulate resistance. Often after enough feedings this way, the snakes will readily eat a warmed mouse dropped in front of their current hide inside the enclosure (not if using loose substrate, though).

Congrats on your snakes (how many will you be keeping?), and you are welcome to come back and ask as many questions as you think of.