Do NOT add oil to the kitten’s milk!!! If he vomits and aspirates, it could get into his lungs, which is very dangerous! This is not very common, but better be safe than sorry 😉 Plus, if you give him too much oil, it could turn into diarrhea and cause dehydration, which can be fatal especially at that age.
If the kitten has been constipated for more than 2 days, the poop starts to get dehydrated, which makes it very firm and hard. An enema with just water isn’t enough to hydrate the poop, so the enema should also contain mineral oil or something. There are certain syrups, such as lactulose, that your vet can prescribe to add to your kitten’s formula. Try dipping the tip of a thermometer in a little bit of oil and inserting it into the kittens butt. It would also help if you added a bit of oil to your fingers and rubbed their bellies. Make sure you stimulate them before and after each feeding, using a soft wash cloth or soft toilet paper or cotton wool (cotton balls may not be enough, cause they’re not as rough as the mother cat’s tongue). I would also suggest to keep the formula/ water ratio as recommended by the brand, as if it’s too diluted, it could cause diarrhea once the constipation problem is over. I would also suggest getting second opinion from another veterinarian.
Don’t worry, you’re doing everything you can for the little guys! Poop problems are a very very common issue for kittens. Constipation is definitely spmething that should be treated as soon as possible, but it’s not like it’s fatal or anything! As I said, don’t add any oil in his food, you just need a tiny bit of a laxative prescribed by a vet. As long as they eat, pee and aren’t lethargic, everything is gonna be okay!
PS: How long have they been constipeted and how long has it been since the enema? Sometimes, it can take a couple days for the enema to start “working”. Be patient and make sure not to give too much oil/ laxative, so they won’t get diarrea!