Give them something that isn't fattening. Frozen grapes are good.

if they are hungry feed them, but remind them that they just ate

My Dad is good with a clock which is on the wall in the kitchen, I reminded him that we had just ate and say we will have a cuppa & something to eat in 1/2 an hour he clock watches most the time, sometimes can stretch to an hour then have a snack. If under weight I would give them something more substantial as I'm sure there were times when my Dad hadn't eaten enough.

There brain can't process what there body feels

We have to give mom a snack but she won’t eat the healthy snacks like fruit. She only wants junk food or carbs like bread. If I leave it out she will eat a loaf everyday. We buy the little chips like school snacks and put out a couple per day. She is getting huge. We hide all we can even the cheese under stuff in the drawers. Like I said in another post she got the bag of pancake mix and was going to eat that with a spoon when my husband caught her. It’s so hard. Good luck