not listening to whoever said it's your line
if all the machines are dropping out .... it's the first common point .... the router....
1 router could be faulty ... but 2????
the router should have a connection indicator - is that going off?
if YES - it's the next common point - the line
(what do the phones sound like? - noisy?
have you got filters on EVERY socket?
can you try the router plugged into the point where the line connects ... (with the rest of the sockets disconnected)
get bt to test the line