Rusty Frame Issues

[73737373]

Some advice needed regarding the best way to proceed. Where the rear coil spring cups bolt to the underside of the frame, has rusted thru the frame and coil spring cup mount support. In that same area, the frame has vertical cracks on the outer sides; about 1/2 inch on driver side, about 1 1/2 inches on the pass side. There are 2 supports on each side that I've removed, also, in addition to the spring cup supports. These supports run along the inside of the frame and are riveted on.

Thoughts? thanks.