RE: Access Team vs Owner Team vs record sharing
Hi,
It seems like your problem has been resolved?
Just as a final answer to your hierarchy question, in regards of BU, I would use a top level BU and a flat line structure for your other BU's under the top one. I would put all data in the bottom line BU's and keep the top level for a time in the future where you suddenly would need a more piramid-kinda structure. A bit more work now, but a lot of work saved in the future.
Also, if you would ever need a user in more than one BU, make sure you default teams created in your BU's are labeled as 'do not use' and create a duplicate team for each team and set your users in the correct teams. That way you can use cross-BU sharing via teams :) .
If however your problem is limited to these two users, I would go with one team for the two of them and set the owner via workflows.
Ps:
in regards of using access teams vs owner teams:
Ask yourself the following question:
Does this record need different users all the time? => access teams
Are the people working on this record changing all the time? => access teams
Will I be sharing all records in that table with a very large group of individuals (performance reasons) => access teams
For predefined ownership and security-role matrixes, use the regular teams :)
Hope this all makes a bit sense?