I have one telephone line coming in. in the house, i have 3 phones running off that one line. sometimes,?

when we get an incoming call, all three phones will ring. the one in the kitchen is an old touch tone, the one in the living room is a double cordless (2 handsets), the one in the bedroom is also an old touch tone. but sometimes, the ones in the living room ring once, then they say "line in use". when i pick up the one in the kitchen, i will get a busy signal. then i will disconnect the line from the cordless, wait a few, then plug it back in, then the dial tone comes back. sorry this is so long....