Plumbing HELP! Main Drain Clogged!?

The main wash basin sink where the washing machine drains into is clogged. The drain pipe it leads into is also the one where the dual kitchen sinks drain into. I guess the main drain pipe out of the house where the wash basin sink and the dual kitchen sinks drain into is clogged. When the wash basin sink fills with water it doesn't drain, but the water back up into the kitchen sinks (the kitchen sinks are about 6 feet away from the wash basin sink). Also, when the kitchen sinks fill with water, they too do not drain, but the water backs up into the wash basin sink. The main drain pipe for all sinks is next to the wash basin sink. The wash basin pipe and the drain pipe for the sinks tap into the main pipe just below the wash basin's drain pipe. The symptom of both sinks clogged and backing up into each other tells me the clog is in the main drain pipe and is possibly below where the wash basin drain pipe and the kitchen sink drain pipe feeds into the main drain. All pipes are PVC. My roommate, being a moron used Drain-O. The pipes are fine, but the Drain-O did not work. We used hot water from the tap, snaked it, and we have tried a plunger on all sinks without any change; none whatsoever. I will try boiling water next. What else can be done? I am sure the clog consists of lint and hair from the washing machine and oil, food particles, and grease from the sinks. Please help! I cannot wash my clothes nor wash any dishes. Sorry if this is a little long-winded, I want to be as detailed as possible. Thank you to all who help.