Go stand in between the lawnmower and the wall in front of the food court and they will try to ram you and get stuck.

Chop the driver with the katana till he dies, then the passenger will jump to the driver seat, and do the same thing.

The guy on the gun you just have to keep moving around the back of the truck and chop him til he dies.

Have a little bit of health just in case he hits you with the gun a couple of times... but it works for sure! Then you can take the gun off the truck!