Ugh, that sucks! But if I've got it right, it might not be hopeless. I believe plants have two systems blocking uptake of toxins, including metals: one between the roots and aerial parts, and one between the vegetative parts and the reproductive structures. So while root crops might
be a bad idea (depending on whether a given species of plant has a high level of chromium uptake) leafy vegetables, and especially fruits/nuts/seeds/flowers, will probably be a lot safer. Also, if Cr(III) is less soluble, the plants might be less inclined to take up excessive amounts.
Would it be feasible to run a test on some of the foods already growing there, to see if they contain large amounts of chromium? Doesn't really matter what the soil contains if the food is ok. Except... the water might be a bigger issue. But I suppose you could go for rainwater harvesting for drinking purposes and use the water from the sources for watering the plants, cleaning, etc.
Also, maybe you could reduce the availability and mobility of chromium in the soil somehow. Here
is a study that seems to say biochar is a viable way to do that. It also seems like biochar can reduce Cr(VI) to Cr(III).
I hope you can find a way to live there. It sounds like an awesome place.