hi delljoy, reading it back it seems you just saw him a few days ago ... (do you have plans to meet up again soon?)
if he is a private man, and severely depressed ... i'm not sure it would help much or be appreciated for you to contact his sisters in these circumstances ... and regarding email; when I've been depressed things like emails ... way too hard and requiring too much effort to think about, or reply to; and can just add to the pressure and the depressive thoughts and ultimatums of any kind don't really have the desired effect of helping
i know this must be incredibly hard for you; and that you need your own support as well and hope you find it here
but from what you've shared I'm not sure following through would help
can you go and see him or is he out of reach in terms of knowing where he is currently?