firstly, congratulations. As the people above have said, your best bet is to sit down with her and properly talk. Get all the problems out into the air just go for it and come up with solutions to them. If you don't talk, it'll only get worse. Do whatever is best for the kids.
You must be feeling a lot of anxiety right now. too Best to try and get things sorted. Don't want things getting worse. Depression can be serious. Feel free to vent on here, we will all listen.
Best advice i can give not being in this type of situation before. I hope it all goes well for you though.