Before I give me opinion I was wondering how old your 2 indoor cats are...4 1/2 lbs and 9 lbs are not big. My little one Vixen who is 1 year old and is quite tiny is 7lbs and Lilith my big girl who is 15 months is double that. She is a little big overweight but the vet said she is very healthy. So those weights are not big at all. So just wanted to know their ages and maybe it would help us too if you could post a pic or 2 of them. That way we can kind of see their size as well.