Hm...which one to get...

I would not change the food of the 18yr old.
As far as the baby, I am not sure why you want to take him off wet food... Wet food is the best food for a cat health wise, and if you want to keep the weight in check, that is the way to go too - feeding more wet and less dry will make it way easier to cut down calories. Dry food is calorie packed, not wet.

DO Not change the older ones food... 27% is fine for a senior cat , 33is a kidney taxer

Carolina is correct about wet food...

wet food 5-6 oz can ave 150-200 calories ...

dry food 1 cup ave 350-400 calories( which in most brand is roughly four oz in the cup)

You can feed Tiggy two wet meals, one in the morning, and one at night, most of his calories would come from wet, and he wouldn't be very hungry, only snacking on the dry food...
I will leave the answer about snacking on Sasha's food to Sharky to respond.

I have three cats: ages 12, 11 and 7 on blue buffalo healthy aging dry, and grain free wet food twice daily. The healthy aging has 32% protein, is that too high? I like blue buffalo, and now I'm wondering if I should switch to a lower protein formula; their weight control has the lowest at 28%.

That could be fine for some.. but read where the protein comes from... Iams used to be a solid food , today IMHO I would suggest cat chow before it...

The younger cat is okay if it samples the less protein food... AFFCO says kitten food only has to have 30% protein... Obviously kitten cannot just eat older cats food but a bite here and there is likely okay...

NOTE I am not a vet either... but I have worked in the pet food industry and learned the AFFCO stuff in and out..
Acceptable yes... advisable no.. Think about a older human , do you feed the same foods to a 90 year old that you would to a 35 year old?

Older cats do not digest the protein in a dry as well as a younger cat... This is why MOST senior drys have less protein and fat .... Now if you are feeding a Quality wet even kitten is okay for MOST seniors as it has the Moisture to aid in proper digestion..Realize "senior" begins for a cat at 7-9 depending on the vet and personal preference... your 18 yr old cat is roughly 90-95( depending how close to 19 )... Your six month old is roughly 6-10 years old...

Many are not to keen on wet .. I have settled for 25% with my current crew... There are all stage foods ( good for kittens thru adult) Most are in the 30-34% range ( grain frees are higher)..

Water drinking for a non wet eater is AWESOME

Wet is definitely best! My girls only get dry food occasionally, or as a treat. When it was a larger part of their diet, they all gained weight--a little known side-effect of giving a carnivor so many carbohydrates. Have you heard of Dr. Martin Goldstein? He wrote a book called, "The Nature of Animal Healing." I highly recommend it. http://www.drmarty.com/drmartybook.htm If you read this book, you would never consider feeding your cat Science Diet. It's crap.

It is Blood work to determine kidneys ( urine helps but only shows one part of the picture)... I dealt with kidney issues for 4.5 yrs with one kitty ... After dealing with it and researching I will NEVER feed a senior cat over 30-32% protein in a dry form.... Oh and FYI 90% of cats over 16 have some kidney disease ...

Why would you have to have a nutritionist call you on how much to feed? It is Definitely something the vet should be able to cover as it is a very elementary item... Kittens at his age need roughly 1/3 to 1/2 more calories than the same size adult

I'm not a vet, but I am a vet tech assistant and work very closely with the vets and techs at the clinic I'm employed at. But, reading what you've written has raised some major red flags -- not only because I work at a pet hospital, but also because I'm a cat owner.

There should be no reason that a vet refers you to a pet nutritionist unless there is a major issue present. And, from what you've already shared, that does not seem to be the case. Any vet or tech can point you in the right direction as far as quantities to feed a 6 month kitten and an adult cat. To start, while the packaging on cat food is not always accurate in regard to feeding instructions, it does offer valuable information. And, while some of that information can be confusing to the "typical" pet owner, a vet or tech could glean a lot of information based on the labeling alone. And, to be honest, no cat or kitten is the same -- there is a lot of trial and error where pet nutrition is concerned. But, that being said, there is no reason to spend money on a pet nutritionist given your current situation (unless there is more to the story). Your vet should be able to get you started on a healthy diet and regimen for your cats and then go from there during follow-ups and the like.

Secondly, I'd be concerned that your vet did not strongly suggest having a senior blood panel done on your older cat. Before making any changes to that cat's diet, it would be wise to find out where he is at from a medical standpoint. Adding additional protein could be hazardous under some circumstances just as taking away vital nutritients can be detrimental. A cat that age should have a full exam, blood testing (CBC, electrolytes, organ function), and a urinalysis done. And, that's the minimum.

Frankly, I'd be concerned that my cats weren't being seen by a vet confident in his or her abilities as well as someone who does not make preventative care a priority. And, add to that the fact that your vet is quick to make a referral for a professional whose services, at this stage in the game, are not needed...I'd be looking for a second opinion. And, from one cat owner to another, that is my advice.

I think this goes specially for Sasha... Any changes on his diet can be trouble at his age... If he is doing well at his diet, with no problems, I would definitely not fix it, aside from perhaps adding a little wet to protect his kidneys... But that's the extent of it...
For the kitten... you have plenty of time... And I agree with Sharky, you should not need a nutritionist for this... really...

Kittens eat a lot more per weight than adult cats... almost double... Keep that in mind - they need lots of fat and protein for muscle and brain development - they are mean calorie burning machines!

General rule of thumb for a kitten is 1 to 2 oz per lb per day... so you have a 6 lb 5-6 month old kitten ... 6-12 oz of canned food...