CONFUSION BTWN ATIS; GND CTL CLRNC AND APPARENT RWY IN USE AT MCO CAUSES CL65 CREW TO CROSS HOLD SHORT LINE OF RWY 18L AT TXWY C. STOPPED IN TIME TO ALLOW B190 TO LAND WITHOUT INCIDENT.

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WE TAXIED TO RWY 18R (THE OUTER) IN MCO TO DEPART. IN DOING SO; WE CROSSED RWY 18L WHICH WAS CARRYING A LARGE 'X.' 3 HRS LATER; AGAIN IN MCO; THE ATIS RPTED RWY 18L FOR DEPS AND THEN RWY 18L WAS PUT INTO THE FMS. AT TXWY H3; THE GND CTLR INSTRUCTED US TO TAXI TXWY G; TXWY J; TXWY C TO RWY 18R. AFTER AN INCORRECT TXWY READBACK; GND RETRACTED TXWY G; TXWY J; TXWY C. WE READ IT BACK CORRECTLY AND PROCEEDED TO TAXI. APCHING TXWY B1 ON TXWY C; WE SAW A B757 ON TXWY R1 TAXIING TO RWY 18R AND ANOTHER ACFT WHICH HAD JUST DEPARTED OFF OF RWY 18R. THIS APPEARED ALL NORMAL. AS WE CONTINUED TO TAXI ONTO TXWY R1 TOWARD RWY 18R; WE APCHED RWY 18L AND NOTICED A BEECH 1900 ON FINAL. SINCE IT IS SOMETIMES DIFFICULT TO TELL IF AN ACFT IS ON 1 OF 2 CLOSE PARALLEL RWYS; ARPTS USUALLY LAND ON THE OUTER RWYS; AND MOST IMPORTANTLY; WE WERE NOT GIVEN A 'HOLD SHORT' INSTRUCTION. WE PROCEEDED TO THE HOLD SHORT LINE ASSUMING THE 1900 ACFT WAS LNDG ON RWY 18R. WITH THE NOSEWHEEL SEVERAL FT BEYOND THE HOLD SHORT LINE; WE REALIZED THAT THE 1900 ACFT WAS NOW ON SHORT FINAL FOR RWY 18L. WE IMMEDIATELY APPLIED THE BRAKES AND STOPPED WELL AWAY FROM THE RWY EDGE; AND WELL AWAY FROM THE LNDG ACFT. NOT EVEN CLOSE. JUST AS WE WERE ABOUT TO CALL TWR TO QUESTION OUR INTENDED RWY; TWR CALLED US AND TOLD US TO CROSS RWY 18L AND TAXI INTO POS RWY 18R. WE ASKED FOR CONFIRMATION THAT HE WANTED US TO TAKE POS ON RWY 18R AND HE CONFIRMED IT. WE WERE THEN CLRED FOR TKOF AND THE FLT CONTINUED UNEVENTFULLY. SOMEWHERE IN THE CHAIN OF EVENTS; THERE WAS A MISCOM. POSSIBLE CAUSES INCLUDE: FAILURE TO ISSUE HOLD SHORT INSTRUCTIONS; FAILURE BTWN TWR AND GND THAT AN ACFT WAS LNDG ON THE INNER WHEN MULTIPLE ACFT HAD DEPARTED OFF OF THE OUTER; OR POSSIBLY THE FLT CREW ASSUMING TO DEPART OFF OF RWY 18R INSTEAD OF LISTENING TO THE GND CTLR CAREFULLY WHEN TXWY LETTERS WERE DISTRACTING THEM. IN ADDITION; THE CREW WAS ON DAY #4; WHEN EXTRA VIGILANCE IS REQUIRED. BESIDES DEP RWY CONFUSION AND 1/2 THE CREW AND/OR CTLRS; THIS COULD HAVE BEEN AVOIDED IF THE CREW WOULD HAVE NOT ASSUMED THE 1900 ACFT WAS LNDG ON THE OUTER. INSTEAD WHEN ANY DOUBT EXISTED WHERE THE BEECH WAS LNDG; THE CREW SHOULD NOT HAVE CONTINUED AND CLARIFICATION SHOULD HAVE BEEN REQUESTED.