Sad cat

Question
I recently adopted 2 6-month old male kittens. I have a 16 and a 5 year old neutered male cat.  I have had the kittens for a little over a week.  I have kept the kittens separated at night but have recently allowed them all free run while I am home.  

The 16 year old is fine.  He has even let the kittens sleep on him.  

The problem is with the 5 year old who has always been skittish.  He is very affectionate with me and my sister but no one else can touch him including my boyfriend who has known him since I first got him.  

He has been wildly hissing and growling (like he does at the neighbor's outdoor kitty when he sees him through the glass door)at the kittens, then retreats to the basement...which has always been a favorite hangout.

I have tried all the things I've read and my vet has recommended...swapping smells, neutralizing smells by wiping everyone down with Febreze and making sure to create one on one time with the 5 year old. I bought a calming collar, that I thought was working because my boyfriend was able to pet him, but now I think it was just because he is in a daze and depressed.   I keep the kittens closed in a bedroom when I'm not home and at night. I also have purchased 2 Feliway diffusers that have been plugged in for 2 days.    

He has returned to sleeping with me, but that's it...no more affectionate "roly poly".  No cute talking. He is eating, but not with the same look in his eyes anymore.

Now has  started gagging. Since yesterday, he acts like he is going to throw up, but doesn't.  He did it 4 or 5 times during the night last night. I took his collar off since it didn't seem to be doing anything anyway and I thought it might be making him uncomfortable since he has never worn a collar before.

I've talked to his vet and he thinks it is too soon to worry but I am really worried.  
Any advice?  I feel horrible!  Thanks!

Answer
Amy,

I have a few questions that will hopefully help me to get a better understanding of what exactly is going on so that I can provide the best advice to help your kitty cope during this tough period of time.

- How long have you had the kittens?
- How old are these kittens?
- Have the kittens been picking on your 5 year old boy at all?
- Is there a chance that your boy may have eaten something he shouldn't have?
- Would you be willing to try homeopathic remedies to help get your boy back on track?
- Have you read my previous answers on new cat/kitten introductions?
- Would you be willing to slow the introduction process down and move back a step or two to help make your boy more comfortable with the situation?
- Have you or your boyfriend been lavishing extra attention onto the kittens that the 5 year old would normally be used to getting?

I look forward to hearing the answers to your questions so that I can better help you and your boy.

Kind regards,

Ali