Does DC1 have local friends to play (french?? - that was what it was called when I was younger) cricket within the backyard? That way you know s/he is safe and is otherwise occupied with someone else, and that leaves you and DC2 for s/he activities or for s/he to have a nap while you grab a book and a sit down. Offer to host the other child the following weekend.
Stop cooking the 3rd dinner! It's one main family meal with slight variations each night depending on tastes. If someone doesn't like sausages, then they get fish or whatever but all cooked at the same time on the same frypan/BBQ etc.
Warn all family members this is starting from Monday night.
Friday nights is pizza or takeaway night and it's your partner's responsibility to either bring it home with him or order home delivery. No excuses.
If he is going to be late, it's still his job to order for you his family and he can re-heat the leftovers when he arrives home.
Speaking of which, if he is going elsewhere after work, more than one or two nights a week, this stops from Monday night as well. If a child is required to be at training on a weeknight, that becomes his job to transport the child there and back while you get the younger one ready for bed.
Why is your partner not at home on Saturdays? If it's to do a hobby, then giving him one Saturday's notice there are two children in the house that are required to be at sport or such like. He takes one, and you take the other. He can Man up and volunteer at the DC1's sport to be a referee or such like, getting his exercise in that way.
If Hubby wants ''time out'' then an equal amount of time is granted for you too and it becomes part of routine. No excuses. If he wants to argue it, send him back to his mother.
Don't enrol the children in every activity they express interest in. One sport per season.
Unless you enjoy playing the PS4 or whatever version that is, get it out of your bedroom.
Audio books are an excellent way to entertain young ones. Kate Winslet did a series my DD had, beautiful voice and wonderful stories. DC2 can sit at the table while you organise the family meal, listening, maybe with a bit of craft or ''felt people'' to fiddle with quietly.
Finally, being at the other end of this I can say when the DC leave home, it's like a slap to the head. While there are certainly benefits, they still cause you to worry. I found out on the weekend DD 23 walks through a relatively empty paddock between her gym, supermarket and home of an evening instead of driving (short distance, I can see her point) but to me, even in daylight, I felt an unease when I went through it on Friday. Can't tell her though...