At least you have one cat that likes collars.

Even though all of mine are also microchipped I wanted them to also wear collars. Everyone wears one except for Sunny. Sunny became so upset and stressed out that he became sick. I didn't realize that this was the cause until I began to think what had changed to possibly stress him out. I removed the collar and he's been fine ever since. That was one very expensive collar.

Pearl and Starr have gone through several collars so far. Now they're wearing the leather safety collars and Ziggy is wearing a vinyl one. These are much stronger than the fabric ones so they're kitten proof.