where to start!!!!
if the system is really a satellite system you will be getting much more than 20 or so UK channels using a 1.8m dish - the BBC has over 15 regional variations alone!
transponders are the tech terms for the frequencies used by the satellite. the frequencies / transponders used by bbc and itv and c4 are free by satellite and you dont need to "buy" them - just have the dish and a satellite receiver! there are about 40 tranponders in use for UK TV.
it may be they are a rebroadcasting system, in which case i would avoid.
or it is a system where they have 20 satellite reecivers (each tuned to a different channel - in the "comms room" and sending a combined signal from each of these recievers to each house - you tune the tv into the relevant frequency - this too could be classed as rebroadcasting.
and sometimes you may find that the existing cable is not a good make or is old and may not be good enough to keep the weak signals....i would get new cable layed specifically for a new satellite system...it may cost a bit more, but then it will not rely on old unreliable cable.
something is wrong with the setup you have been quoted for - get another - try broadbandcostablanca.com (sometime trade under nortons) and ask for michael..as they cover your area.
ideally you need a big dish, with a quatro LNB, connected to a system of multiswitch distribution units.
each house will have their own cable from a multiswitch and thier own satellite / sky receiver - so they can chose which of the 200+ free tv channels they want to watch.
if the individual houses want to subscribe to the sky pay tv channel then it is up to them to get a sky card and pay per month.