If you're looking for a meeting place or a good stop around ½ or halfway between Saint Helier and Octeville, you can try Coutances, France, which is about 2 hours east of Saint Helier, or about 2 hours south of Octeville.
About ⅓ or a third of the way, you can stop at Granville, France. This is about 1½ hours southeast of Saint Helier.
If you drive straight through without stopping at all, the total distance is 165 km. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 3 hours, 60 minutes.