You're off around 1/2 the month. I'm willing to bet that's not in a row. You CANNOT BE the primary custodial parent when you have no one to care for the children when you're working (and you've stated there's no family to help you) and Mom is fit to provide care. BEST CASE, you get a schedule that allows you to see the kids when you're off, and is close to 50/50, but that's unlikely w/out Mom's agreement.
You're not going to get an order that forces Mom to sit around waiting for you to have time for the kids.
And that's 100% irrelevant in court. It's no different than a married woman being a stay at home Mom so that her husband can work a wonky schedule. There's no way in H*ll you can afford a nanny, or even a place w/enough room for a nanny, or you'd already be doing that. So Mom might be financially dependent upon YOU, but you are dependent upon HER as well.
You can yell at me all you want, but all that history? It matters not. You still leave the kids with her for days at a time while you're working. She's fit. End of story.