The short answer is that there’s a really strong chance that you’ve got 2 conductor wire with no ground going to the receptacles if they’ve not installed electrical outlets with a third prong. Fixing that would require running a ground cable to every outlet so configured which means cutting a lot of holes. All things considered I’d probably do a re-wire at that point. It brings into question the type of wire used and the safety of the electrical panel etc. These things age, and standards change.

I would personally want to check the receptacles that have a ground to make sure that the ground is actually hooked up to something and that it is not simply connected to the neutral, which are both bad things.

Given the variables, you’d be best to consult a professional.