Same issue here. One Google account with subscriptions to family member Google calendars and those subscribed calendars do not sync with the Tidbyte 
+1
any updates? it does seem like adding calendars in separate instances could be a temporary workaround.
I looked for this app in (community/apps at main · tidbyt/community · GitHub) but couldn’t find it. Does anyone know where the source code is?
Did this ever get resolved? Its happening to me (I just received my first TidByt (gen2)) ?
This really needs a solution. One of the reasons I backed the original Tidbyt was to have an easy way to glance at my upcoming events. I just received my gen 2 and this still does not work - only events from my default calendar get displayed. This is pretty bad - it makes the calendar integration pretty useless. A solution is needed. Please prioritze this.
Got my gen 2 TidByt and immediately ran into this issue with my family calendar.
Is someone working on this? Or is the Google Calendar app code somewhere public that an outside contributor could help?