Max's invulnerability is actually 2 layers. A (almost) skin tight force field. And another layer of defence.
As she has survived having her field breached.

We dont know how Hiro's invulnerability works no. Except it has soaked up some fairly solid hits and immense pressure.
Sonic absorbtion seems a seperate thing.

The same with Stalvart. We dont know how his invulnerability work.
Density control seems a seperate ability. That likely dont quite explain his degree of invulnerability.
At 4 dots he is just a point below Thor/hulk tier.