Got 4 cats now, one is a 3 month old that has just been integrated into eating in the same room as the older 3.

Issue is the eldest cat 13 year old has a thyroid problem which means at times she is a bit off her food and drinks alot (she is on meds twice a day and monitored by vet bi monthly now)

What we have noticed is the eldest above really likes the kitten biscuits and prefers this to her meat.

Is is ok to give them all kitten biscuits as well as their meat feed twice a day?

Age range is

Tashi 13
Winnie 12
Hattie 1
Tiffin 3 months

Question is is the kitten food biscuits ok for alll of them.
Thinking of

breakfast meat

lunch kitten biscuits

tea meat and kitten biscuits

Any advice welcome Tashi is thin because of health and sometimes just won't eat...

for Tashi I would use chicken and fish to help build her up. My friend has a cat with the same problem , weight and we built her up by feeding her separately, she had both buiscuits and fresh meant for a few weeks , she is now happy on her diet , we still feed her sparately and always stay with her, while she eats. She loves fresh chicken too

Kitten biscuits are usually much smaller than adult ones so easier to digest and crunch- foods specifically for senior cats tend to be softer than adult foods but Ive found my lot won't touch Science Plan, I have to try lots of different samples before I find one a particular cat prefers. When you have a multi cat household, trying to feed a specific food to a specific cat can be a nightmare so I've stopped faffing about and now mix the completes (yes, I know they are all indivudally formulated) so that there is a mix of kitten, adult, senior and dental care and leave it to the cats to munch- I only buy Royal Canin/Burns/James Wellbeloved or similar quality (but they just won't eat Science Plan) completes and since mixing the RC oral sensitive dental biscuits in, have found they are more likely to get eaten than they would if I put them out separately.