Like Jim said, how comfortable are you with welding? To be honest unless you're a professional fabricator I wouldn't feel comfortable with it. We're talking about how your kids seat secures to the vehicle, imagine what one weak weld would do if the vehicle were in an accident. If you feel comfortable you could probably put a drop bracket on the front of the seats and move a few of the pieces around on the floor and make it work. Only question would be if there is reinforcement under there to make sure it's secure and if that same reinforcement exists where you plan to move them to.