How can I sync vault in team without 3rd party apps

Things I have tried

sync one vault between at least two team members on different devices without 3rd party apps from different Obsidian accounts.
I could only sync team members on different locations via logging in in the same account.

What I’m trying to do

I want to access one vault via different Obsidian account without 3rd party software.

If this is not possible how many devices can access the same vault?