GRBL treats the homing and hard limit switches the same. You don’t need to have separate switches. Just add them to both ends of each axis and configure GRBL with homing and hard limits. I currently have this setup on one of my machines.
Oh, I didn’t read back far enough. Sounded like they were just wanting to setup hard limit switches. Didn’t realize they wanted something more than that.
As a side note, I have had occasional issues using the hard limit switches. It would just randomly trigger the switch during a job when it was nowhere near the switch. Could have been electrical interference, bad switch, bad wiring, solar flares, who knows. Something to consider though.