Any chance you can incorporate #1 child into some outdoor activity
@Rorschach? Young kids are really hard work at times, but even simple things can amuse them for hours too. Not to diminish your own internal battles at the moment, but if new bub is due within the next 4 weeks, I'd be guessing that your missus is probably over being pregnant about now - maybe give her some time out by taking your young one out for a walk to the park, kick a ball, chuck a frisbee etc. Get some fresh air and exercise and slow down for a bit as
@PJO says, and it might help if there is any tension at home. In my own experience - and this sounds silly - getting enough sun is important, particularly as the days are getting shorter; the winter blues won't help your current state of mind.
I've got a saying that I tell my daughter (high function autism) when she gets overwhelmed by everything: "only worry about stuff you can do something about" - some shit is going to happen no matter what, so why stress about it. And if you start something, try to finish it so it's off your plate and one less thing to worry about.
Good luck with it all mate - don't be afraid to open up and tell people how you're feeling, even if it is a bunch of strangers online. Most of us will know what you're going through.