For this, I wrote, "Will they play tennis?" and it was marked wrong. But can't it mean both "Will they..." and "Do they... (regularly)? I didn't report it, because I'm not sure.
Yes, i think it should have context like "a h-uile latha". It's an awkward one, as in english "do they play tennis?" can also mean "do they know how to play tennis?" as well as "have they played tennis regularly in the past?"