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"

Nope, because बिल्लियाँ is feminine. कितने is indeed a word, if that's what you meant, but it's used for either masculine/mixed plural