I started my 4 cats on scheduled feeding. Based on their weights, they're supposed to be getting 2/3 cup, twice a day. I give them a super tiny bit of wet food in the morning, followed by their dry food. I leave it out, portioned into four bowls all day. By night time hardly any food is gone, so they aren’t getting 2/3 twice a day, but less than that and only once a day. They are really big and fat, about 17-20 lbs (7.7-9.1 kg), so they desperately need a diet; but now I am worried they aren’t getting enough food.
You have already taken some important steps when it comes to helping your cat lose weight. Besides what is in my answer you can always ask your vet for advice on diets and how to apply them.
With how you described the situation you are trying to feed less but the cats do not eat the new food. You can help your cats get used to the new food by transitioning for 7-10 days. Give them less of the old food and more of the new food gradually and make sure they have plenty of fresh water available. Cats are creatures of habit and it might take some time to get used to the new feeding schedule. Information on transitioning from the mentioned food ProPlan.
If this does not help and your cats are still not eating the new food you can wait a little but not longer than 48 hrs. You can try different foods or maybe even their old food - but less. Just like humans, cats need to eat less calories when dieting. There are ways to calculate how much food they should be getting.
You can try canned wet food since that usually has less calories than the same amount of dry food.Tips on how to help your cat lose weight.
If your cat does not eat wet food that is not an option for that one but maybe the others. Please also be aware that wet food can be an important factor of keeping your cat hydrated.Why cats should eat wet food too
If you want to support weight loss in your cats further playing with them is a great option. Sometimes a simple laser pointer can be enough to burn some calories.