pre-filling daily feed amounts works great of course. In this day and age everyone has a smartphone with a camera. If you don't want to fill lots of little cups, put a single feed's amount in a shot glass and take a picture, then text it to them. Just tell them to match the picture. As long as they're close it'll work. If you can't trust them to do that, not sure I'd trust them in my house at all.
This is an extra challenge for smaller tanks with few fish. My tank's big enough when I leave the instructions for my son is "one cube of frozen food a day". I usually have a mix of frozen brine and frozen bloodworms in the blister packs, and one cube is enough, they'll be ok on a diet for a week. I overfeed anyhow. It would be harder for a small tank. My nano is shrimp only so they can get a algae wafer mid-week and be fine.