I'd rather suggest using a single portal that display documents from a relationship filtered by group(s). The question then would be how to present the user with a selection list. There are a number of ways, some of which could even give you “tabs” …
You could …
… use a value list with your groups to set a selector match field, e.g. via a popup, or as a checkbox set to select multiple groups via multi-line key.
… create a table to hold your existing groups (and add new ones) and display them in a portal via a Cartesian relationship. Use Conditional Formatting to give visual feedback as to the current selection(s).
… simulate tabs by displaying a horizontal row of single-row portals (with incrementing initial row); adding a new group to your groups table would automatically create a new "tab”, provided the (invisible) portal is already in place.
… do this with a (calculated, set) repetition field instead.
… present a list of your groups as links in a Web Viewer (and style them in a “tabbish” way ); use the fmp:/ protocol to trigger a script in the database.
… [ probably more ]
Adding to erolst's lists:
… if you are using FM13 you might create the right sort of effect using Slide Panel objects with varying visibility conditions