How unfortunate that the kittens died, you have some hypotheses, like the toads, but, it is only a guess. You must be attentive to know the real reason and avoid future deaths. What a pity that you don't have veterinary help, this situation is worrying, you really needed it, maybe it would have helped you to find out the cause of their illness and even save them. Greetings.
RE: Only one made it through 2023.