I’m assuming as he told me he pays for multiroom that he as a feed into all 3 rooms already (will find out for deffo)I have 4 boxes, although only 2 really used, I use bt homeplugs to connect to the router to save having wires running round everywhere. Does he have cable coming into the three rooms already? if not he will need to split the feed that is coming in to the flat so it can go into each of the rooms.