Have you tried setting up the problematic RF kits to have different IR outputs from the other kit that is also having the problem?
i.e. Bed TV is having the above listed issues with the Bath TV. Enable IR routing on the programming for both and set IR route for Bed TV to say 1 and IR route for Bath TV to say 3?
Yes plasmas will interfere with all kinds of other devices...I doubt it would cause the problems you are having since you claim that each device works great by itself.
Removing antennas was something we started doing back in the good old days of the mrf-250 and carried over to the somewhat less than reliable mrf-300 (compared to mrf-350). Removing the antenna on the mrf-300 yielded FAR superior results but limited the range a bit.
We don't use the mrf-260 at all so I can't comment on that piece. We use the mrf-350 and msc exclusively with URC systems.