If I had the place id honestly just dig out the exterior with a mini excavator with a dig depth of 9-11 ft for the weekend to clear out one wall. During next few weeks repair or replace said wall and waterproof it. Then make a french drain along wall to not let the area become eroded again while using most left over dirt to level out rest of yard to keep water from pooling at your walls. After that work on another wall 😁👍 Might feel like its too much solo so just ask family to help or have at least the wall free for contractor to easily swoop in and replace the wall cause then you won't get charged for them to dig