What a pain
If it is found that handsets interfere with TV signals. Given the remoteness of the properties that can't be fibre connected, I assume that any interference is going to be from within the same premises. If that is so, I would guess that a number of ways exist to reduce or eradicate the interference.
First would be a filter on the back of the tv, back in my Ham days I found that to be very effective in most cases.
Second, I assume that the handsets in question are telephones, now if the telephone is a fixed phone as distinct from a mobile phone. A yagi antenna pointed at the TX/RX tower should keep most of the signal away from the TV antenna which is probably a dish pointing upwards.
If the telephone's of of a mobile configuration, then the only answer in the event of interference problems is to keep the calls short or turn the tv off. Or move away from the tv or tv antenna, inverse square law and all that guff.