We have a grazer (who is also picky) and an over eater at home. To control their food we had to give them more, smaller meals each day. Here is our feeding schedule:

Breakfast: split a can of wet cat food between both cans (3.2oz can) - between 6-7am Lunch: a scoop of dry food into a bowl each (don't really know the size, maybe a half cup) - around 12pm Dinner: split another can of wet food - between 5-6pm 2nd dinner: a scoop of dry food each - between 10-11pm

It's not perfect as sometimes the over eater will get a bit more food, but the restrictions do help keep a schedule for them. When the grazing cat finishes only half their wet food, we often give the rest to the big guy. The dry food is also an appetite control diet, but the over eater still goes to town on it.

The picky one sometimes doesn't eat the wet food and wants dry food, so we save the half of the wet food for the other one's lunch.

Experiment around, see what works and what doesn't. Maybe try an appetite control food, it is a bit pricier but may work for you.