..... probably more than 50 feet.
The more than 50 feet isn't a problem. It's just
how to do it. I'd use the DS10A door/window sensors. But I'd remove the magnetic switch [reed switch] and extend it using CAT5. that way I [you] could get the other part (that holds the batteries and sends the signal) really close to the monitoring area/computer/CM15A interface.
Then I'd use the standard AHP software along with the OnAlert software plug-in. I'd create a macro that reset at midnight and cleared both restrooms of any occupancy. Then when the DS10A senses a door open it would toggle (a conditional macro). I would create the same macro for both restrooms.
My way is not the only way to accomplish what you want to do [
by any means].
dhouston has great examples of how to extend radio range and reception.