As for "life's too short", what about pointing out all teh things he's missing out on by spending too much time on video games as opposed to living real life, and pointing out that life is too short to miss these opportunities, childhood is too short to waste?
A thousand times THIS!
I'd be gutted if my DCs didn't want to run around outside. There's a lot of simple pleasures that can't be appreciated with your nose in a game.
I think you'll have to somehow work things out so, as others said you help deal with the fall out. Because there will be one! And it's going to be very difficult for your DW to deal with alone.
I think the screens in the morning should go, though. Is he getting ready for school before he's allowed on games? If not, and if getting ready is a cause of strife every morning , perhaps letting him go on his game ONLY when he is completely ready would be a fair compromise?
Other than that I can see why games are being used as a babysitter when your DW has so much to deal with. So can you rearrange things to make it easier when you aren't there?
A few suggestions:
Bulk cooking/freezing on weekends so less time cooking after school
Changing order of housework so more is done after DCs are in bed so there's more time for DW to have fun with DCs in the afternoon
Taking DS out for a quick walk as soon as you get home to get some exercise/fresh air
New bedtime routine for wind down time (no screens after dinner), bath stories etc that you can do once you're home