Is the swelling less the third time with Kybella as you have less fat?

You are correct.  The swelling will likely be less during your during Kybella treatment because you have less fat to treat and you will require less product to be injected.  Best of luck!

Typically with each treatment less product is used due to the fact that there is less submental fat being treated.  With each treatment, you can usually expect less and less swelling.  Good luck and enjoy your Kybella results.