Creating a complicated table

I’m trying to make a table with these parameters:

• 4 columns
• Individual cells in columns 1–3 (like “expected shipment date”, expected delivery date”...)
• The table has to stretch horizontally proportionally with content always staying in its columns
• Columns 1–3 are grouped with the border

I don’t see how this is achievable in an adequate way. The way I did it now is having a second table underneath just for borders for columns 1–3 (“table 2” layer). 

With one layer it’s only possible to:

1. Sacrifice grouping columns 1–3, then each cell will have it’s own border.
2. Sacrifice stretching, then you can just adjust the cell’s border.
3. Group columns 1–3 and use auto-stretching auto layout inside, but columns won’t stretch proportionally.

Do you see any way to achieve that?

Also attached the recording of how it’s stretching. It’s working, but like I said the second layer adds complications.