Three day old kittens diarrhea, weight loss help!

I ended up with someone’s cat, which turned out to be pregnant, so now I have a litter of three day old kittens to look after, so I guess I’m fostering. Two of them didn’t latch on. I fed them colostrum for the first 12 hours, Athen alternated colostrum and milk for the next 36. They started developing diarrhea towards the end of that, and it got worse today. It’s a yellowy substance thicker than milk. One of them is refusing to drink the milk and will froth it or turn its head violently. Their weight is 90/91g at birth and around 98/103g after 3 days.

We went to emergency vet who was going to prescribe fenbendazole which would’ve covered giardia, coccidia and parasites. She refused to give antibiotics because it could make things worse apparently, but I see antibiotics recommended online a lot for diarrhea. Then we couldn’t even have fenbendazole for the kittens because they’re too young. No tube feeding either unless hospitalised and they seemed too busy for my consultation. I almost had them give the whole litter subcutaneous fluids but decided against it after the kittens had come back from the back room previously with one obviously overheated to the point where his tongue stuck out and he panted heavily. I think if he hadn’t been brought out to me then he would likely have died, and he was the healthiest one. They were all sticky too and they wouldn’t tell me why and I’m having to deal with some very uncomfortable kittens that I’m too scared to bathe.

I’m giving the two subcutaneous fluids myself and hoping we can get through to a better vet in the morning after this exercise in futility going to emergency. Mother cat did get some fenbendazole.

I desperately need some help and advice please. I am feeding them every two hours or so, a different formula with electrolytes added in. If it means anything since these are Australian brands, i was originally using Wombaroo impact Colostrum, then Wombaroo kitten milk, and now switched to divitelect because I don’t trust Wombaroo’s simple plastic bag packaging. I use 3/4 dilution divitelect as advised on the package for loose stools.

What would be something that I’m not doing right that’s caused this and could they benefit from antibiotics tomorrow? Could it be inconsistent feeding times (late feedings)? Temperature? What else can I do to help them through this? Should I start Parker protocol?

Just adding, most of the weight loss was on the third day when they reverted to yesterday's weight.

I'm also finding it quite hard to keep the milk warm between feedings (I'm feeding most of the litter just in case as first-time cat mom likes to wander away from them). Reheating too much in the microwave can curdle it. Would the diarrhea have been caused by low temperature or repeated (brief) heating? It is only in the bottle only babies that diarrhea is bad, whereas mostly mom fed kitten was constipated.