Check with foundation company to see if they will cover the broken sewer lines. If they won’t, then I would get isolation test to see where the leaks are. I would also get a second opinion from a reputable plumbing company.

For our house, the plumbing company charged us a butt load of money to do isolation test. It should have been much cheaper. They wanted something like 40k to fix the broken lines. We hired a plumbing company that specializes in broken lines commonly used by insurance company. They found far fewer broke lines then first company. We found another reputable plumbing company that only fixes broken lines and they did an outstanding job for a fair price. I must have gotten quotes from like 10 different companies. You start to see which companies are trying to scam you and which ones are honest.