What is wrong with Žerou mouchy tvoje kočky?
It is somewhat less common, as it can be confusing without careful (and strongly stressing) intonation, but it is possible. I will add it.
Thanks. Why would it be confusing? Could it mean Do flies eat your cats? with this word order? So many native Czech speakers tell me proudly that word order doesn't matter in Czech, but it certainly does!
Normally one expect the SVO order. OVS is possible, but can be sometimes surprising where both can happen. Cats can eat flies and flies can eat cats, so there is a risk of confusion present here.
By reading this sentence: Žerou tvoje kočky mouchy?, could it be grammatically correct to translate it by: Do flies eat your cats?
I do not like the present simple. It does not make a good sense to me. But with present continuous it may be fine.