I'm not going to speak to the intercepting of the plumbing but you will need a vent for your new bathroom and you're going to have to run that to the outside. That is a plumbing question though. As for breaking up the concrete that isn't all that bad as long as you have a good back.
You can use a cement saw or your can bust it out with a large jack hammer. Really depends on the thickness and strength of the concrete. Then carry the concrete out. You'll be laying the new pipes in your trench. You'll need to back fill with sand and then concrete.