Doubleheading is something I've never seen done with the radio throttles. A friend has a very large layout, and used them for many years without doubleheading. Each of the (black) throttles will control two engines, but on different tracks. All the radio throttle does is vary the amount of power that goes to the track. Like using a power pack knob by remote control. So I don't think it would work for doubleheading.
Crest also makes radio control units that fit into an engine, you control it by radio. Another friend had one, but the circuit board was pretty big and would not fit properly into a Bachmann 2-8-0 tender. I think they are marketed for large scale trains. Also it needed its antennae strung out a fair distance along the train. Not really practical I think.
Why not just go with DCC, a lot simpler.