"How many cats are there?"
Translation:कितनी बिल्लियाँ हैं?
Verb endings in present simple only end with ता ते ती. ती is used for all feminine subjects, whether they're singular or plural. This applies to a lot of question words as well, कितनी, कौनसी, किसकी, used for feminine, whether singular or plural. बिल्लियाँ कितनी हैं would be "How many are the cats" instead of "How many cats are there"
And btw if that's case then what's the difference between yeh kitna hai and kitna yeh hai ?