APFS Containers - Encapsulation and Safety
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.