The easiest way to repair copper pipe is to use Sea Tech fittings and plastic pipe. As long as you can get to a Good Round section of the copper you can cut it out with a small tubing cutter and slip in the new section.
As for finding the leaks I would drain as much water as you can and try and get a compressed air source and apply about 35 lbs of air to the system. You should hear the leaks and hopefully be able to get to them.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles