if I upgrade to catalina with my imac will I beable to sinc with my mac book pro with High Siera

I am using a mixture of OS versions between home and work. The only gotcha I found was with Reminders. Reminders go a big update and the old isn't compatible with the new. This doesn't affect me personally because I use Things for reminders but if you do make the switch, be sure not to select the Reminders upgrade. (This was initiated on my iPhone but I assume you'll get the same prompt the first time you run Reminders on your Catalina Mac)

Yes, you should (assuming you are looking at apps like Mail, Notes, etc.). I have exactly the same situation with my MacBook Air that is on Catalina and it syncs well with my iMac which is on High Sierra.

You should be more specific as to what you’re referring to by syncing.