Multi-way sync with multi calendars

I’m looking to migrate away from Google - aren’t we all!
Here’s what I’m trying to do:
2 way sync between google calendar and NC Calendar.
2 way sync NC Calendar with Android
2 way sync NC Calendar and thunderbird/Lightning or vCalendar (Claws-mail plugin).
The idea is to use NC calendar as the main server calendar and sync everything to it. Need Google Calender at the mo as others use it too.
I can sync Google calendar into NC calendar, but not edit in NC or sync back to GC.
Unable to access GC in NC from Android!
Is what I’m trying to do possible?

The core-functionality of Nextcloud is to keep data private. Syncing data with Google is therefore counterproductive. If you publish a Google calendar its data is “read-only” and only displayed within Nextcloud and not a 2-way sync.

As long as you use Nextcloud as the central calendar instance a 2-way sync with other clients like Android (DAVx5), iPhones, Thunderbird/Lightning etc. is possible.

Thank you for your quick & succinct info.
The only way to migrate from Google is suddenly or one calendar at a time! Umm…

Transferring address books, I like to use a program (thunderbird) in between, which can deal with both accounts at the same time and which lets me drag&drop all contacts very easily.

With calendars, however, that does not seem very helpful, as it is often hard to select multiple events. The export/import (ics) for each calendar seems to be a more reasonable method.

May be the hint helps somebody anyway who can come up with a nice work-around.