Since I am still using InDesign CS6, I may have misunderstood what has been said already in this thread.
But it occurs to me that a possible solution would be to have a simple 2-cell table that runs the full width of the page. Then build a new table in the left cell and another in the right cell. If the simple 2-cell table had a cell inset of zero (except, perhaps, as outlined in my next paragraph) and a stroke weight of zero, then it would not appear in print (or in a .pdf) and the two additional tables would appear to float within its space.
If you want there to be a “gutter” between the two additional tables, then the cell inset to the right of the left-hand cell and to the left of the right-hand cell could be adjusted to create the necessary gap between the two additional tables.
From having tried it out, I have learned that you have less headaches if you set up ALL the details of the initial table before adding the other two tables. Otherwise you find yourself going back and adjusting things too many times!