i rewatched Prom last week.
imo the xeno's incorporate the dna of their prey into their own. this solves the mouths and chemical issues. as long as they are hunting compatible prey, they should be capable of doing their thing.
of the species shown as options, the xenos freely attack humans, predators and engineers. i dont think they are shown to actively seek out the cats. and they leave themselves, hybrid ripley and androids alone.
the cats bit strikes me as weird.
the androids are not dna based (afaik)
i assume the engineers created the predators, its not clearly addressed that i can find. if not then things get more iffy / weird.
an engineer seeded 'life' (the scene in prom showed plants already here (they did a decent job of not showing it, but they clearly had it, to include modern trees that are a pretty recent thing), at least thats what the xeno wiki says.
so, cats and people are both descended from engineers. why would the xenos leave the cats alone? do you have to be at least 4ft tall for them to target you?