High current buck converter has excessive ringing and poor regulation
It's your layout.  You're going to have to redo your layout and do it more expensively. All your other concerns are not without validity but this is at the root of things. None of the other things would cause ringing this bad.

Have someone else review it before you send it in next time.


Your currents are already really big so all the parasitic
inductances matter more.
This is a 2-layer board with no ground plane (unless I'm seeing things wrong) so the return current loops are inherently large. but you aren't even taking advantage of both sides to minimize loop area. Your routing has huge loops in it.
Your gate damping resistors are not located as close as possible to the MOSFET gates which allows a bunch of ringing between the gate and the resistor.
Your gate driver is too far away from your MOSFETs to begin with and the routing is suboptimal for current loop area.
All your caps are too far away from where they need to be (as close as possible to the IC and MOSFET half-bridges). How is C1 68uF anyways? It's the same size as all your other much smaller caps.