, each one feeds up to three rooms and each room has two coax sockets to plug a TV if needed (to move TV about the room ).
If I've understood right, that may be your problem. If you split the line into multiple spurs using passive splitters ('tee pieces') then the broadcast signal reflects off the end of each spur, back into the wiring, which can cause corruptions with a digital signal. If you look closely at the analogue TVs this may also cause 'ringing', a bold outline to the right hand edge of everything on screen. Ringing is just like the more familiar 'ghosting', except the ghost is only a fraction of an inch to the side, so is less noticeable.
Fitting terminators to any unused sockets may help as they'll stop the reflections. But they'll also absorb some of the signal strength, possibly leaving not enough for the digital sets. Worth a try?
edit: said 'attenuators', meant 'terminators'.