Note9: Can you sync DIFFERENT calendars on google calendar and samsung calendar at the same time?
Candl Apps makes two calendar widgets - one called Calendar Widget: Month and another called Calendar Widget: Agenda. 

You can add calendars to these widgets which will not automatically change the visible calendars on other calendar apps.

Here are the links to the play store:

Month
https://play.google.com/store/apps/details?id=com.candl.chronos

Agenda
https://play.google.com/store/apps/details?id=com.candl.auge