APFS Containers - Encapsulation and Safety I'm eager to use Containers not Volumes on APFS to add beta versions of macOS to my dev machine.
I want as much separation and encapsulation as possible because I don't want the OS's to interfere with each other.
I have read that multiple betas on separate Volumes on the same APFS Container can cause issues.
Thus I was aiming to make multiple Containers on the same internal disk.

Is adding and removing Containers through disk utility safe and effective? (Apple seems to only champion Volumes in it's docs: https://support.apple.com/en-us/HT208891.

Is using Containers in this way providing maximum encapsulation from a logical perspective? (to avoid issues like this: https://www.reddit.com/r/MacOSBeta/comments/hea72p/warning_do_not_install_big_sur_on_the_same_apfs/
In answer to your questions:
Yes, you can add and remove containers without causing problems. You have to be aware that two containers cannot share space in the same way two volumes in a container do.
It is probable that this would totally encapsulate the two OS installs, but be aware that until Big Sur we thought the same about different volumes in a single copntainer so if it will continue to work after Big Sur in subsequent beta versions is an open question.