Whilst I admire your dedication, slugs aren’t their favourite thing to eat and I don’t think they like the larger ones anyway. Luckily it is the smaller ones that reputedly cause most damage in the garden, but they are much harder to collect.
It must have been distressing finding the malnourished hoglets, but mealworms are not the answer. You suggest feeding the hedgehogs mealworms pre-hibernation. They will simply not put on the right sort of fat they need for hibernation on a diet of mealworms. This very likely would lead to them not surviving. If you continue to feed them mealworms, you will be doing them more harm than good. They should only ever be used in very small quantities as a very occasional snack. As you will have seen from the video, many recommend not feeding them at all and that is probably safest. You have heard about the dangers. A disabled hedgehog is unlikely to survive for long in the wild.
If you want to feed hedgehogs, give them cat/dog food, cat/kitten biscuits, or hedgehog food and no mealworms. if they are hungry they will eat it. If you are still providing mealworms, they will very likely show a preference for those. It is like humans with crisps and chocolate.
This time of year is a good opportunity to offer them something more nutritious. They will be hungry when they return from hibernation and if you offer them some nutritious food they will likely tuck into it. Please don’t be tempted to give them any mealworms at all, or you will be starting the cycle off again.
Please always provide water.