batwister,

Good for you to be photographing socially important issues, like this place that caters to people with mental health issues. I think you should do what you are doing, and just improve the process. You know simple things like going in repeatedly, getting permissions squared away beforehand (If possible. That might be a tall order). Shoot the general facilities without subjects to see how the lighting works. Meter before you engage the subject and compose the shot. Little things like that might lead you to being able to focus and shoot when the time comes.