When I started this, I had no idea how it was going to end. I had a list of possibilities, most of which were miserably unhappy. I'm very happy I managed to find one that didn't involve any deaths, nor Harry being carted off to St Mungo's.
I figured Snape would cooperate with Arthur & Hermione as much as he was legally required to, but not the slightest bit more, and he'd let them know how little he wanted to deal with them. Oh, and that he'd let them ask pointless questions and offer explanations he didn't need for as long as they wanted to, to distract them from Harry.