dealing with. Pull into the alleyway (don't back in), and try to turn to the left as much as you can before hitting the event arrow there. This will give you great placement for what's to come.
It appears Jacob's paranoia wasn't completely weed-induced. The new guys he's dealing with did indeed try to take his money without handing over the goods, and Jacob calls you to let you know they're making a run for it out of the back alley. As you see them run out of the door and towards the far side of the alley, you'll realize why we told you to turn to the left. Begin driving towards them, using your car as your weapon to run the three foes down. Don't get out of your car, as these three guys are packing heat. The car will give ample (though not complete) protection from bullets. The red dots on the map represent their location (if they're close enough to each other, it'll be one red dot). Run them down, being absolutely sure they're dead, and then pick up Jacob when the game tells you to.
Follow the GPS' route on your HUD back to Savannah Avenue, where Jacob will be waiting for you to pick him back up. Beep the horn to get his attention if he doesn't immediately see you. Once back in the car, he'll order you to head over to Meadows Park, which is slightly to the east. The drive isn't very long at all. When you arrive at your destination, you'll quickly realize that Jacob has more plans for you and he.