All you have to do is get a sub machine bun from the Paradise Plaza or get snipe rifles and shotguns from the North Plaza... (sniper recommended).

Then you go into the courtyard and just climb up on one of the picnic area roofs, just shoot at them a few times and they will drive to you...

As they repeatedly ram it, take out the gunner first, then just shoot the others in the head and you should win easy!