How to publish an extended version of a Springer journal article on arXiv?
For A, I think the introduction should make it clear that each team contributed to a particular part of the document, moreover, each team should have the opportunity to review/comment/improve sections by other teams, this should help address concerns regarding 3, thus, lead us to favour options 1 &amp; 2.

Option 1 appears to be the easiest option, because problems might emerge during option 2: B might have copyright issues (because A was published first and is subject to copyright), and addressing these issues (e.g., perhaps by attributing content in B to A) is likely to be time-consuming.

On this basis, I recommend option 1.