Chances are there is a splitter somewhere between your external hookup and the two TV's. If your stereo is setup to play sound through the TV, chances are good the split is done there in the radio cabinet area.
I've had mixed results. Current RV the wiring works wonderfully and signal is similar strength to both TV's. In Other RV's I've been in or owned, one TV seems to always have a solid connection while the other always was borderline usable.
Usually either a poorly connected cable or a poor quality splitter being used by the manufacture. Occasionally I've read of a feed wire stapled or skinned with nail/staple gun damaging the wire to the point it was troublesome.
First two solutions are easier to identify and solve, Last one (Bad wire in a wall somewhere) usually a little tougher and some just run an extra wire through a window from a splitter outside the camper.
2020 Chevrolet 2500 LTZ, 2019 Forest River Wolfpack 23Pack15, 2014 EZGO Golf Cart.