There is some discussion of how to use the Apple Watch with your iPhone in the following thread (and I’m sure that there must be earlier threads, too, but my own experience and questions are in the link). Bluetooth solutions: Differences between Made For iPhone, Android ASHA, BT Classic - #16 by jim_lewis
You should be able to pair your Apple Watch with the KS10’s but I don’t know if that will allow you to do decent hands-free calling. I could pair my Watch to the ReSound PhoneClip+ streaming device and make a hands-free call to my wife. Her voice sounded great in my HA’s, my voice through the watch microphone (or from PC+ to watch? - never determined which) through my iPhone 6S to her phone sounded nice and loud but all broken up - mentioning this experience as a comparison as my Apple Watch was connected to the PC+ through classic Bluetooth when attempting a phone call using my Watch as both transmitter and receiver. Bluetooth solutions: Differences between Made For iPhone, Android ASHA, BT Classic - #27 by jim_lewis In my case, there was a long chain of HA’s to PC+ to Watch to iPhone. Using the cellular LTE on your Apple Watch, you should just have the chain HA’s to Apple Watch via classic BT, then out to the network directly, no iPhone connection or other intermediary device needed.
Give it a try and let us know how it works as I’m interested in the KS10’s as a possible new set of HA’s when my insurance coverage rolls over this coming fall. With the Watch using classic BT to communicate with your KS10’s, I should imagine it’s going to be very hard on Watch battery charge.