Dealt with Olshan twice. They told me I needed 20 piers at one property. Next company came out and said I needed none (problem was ground had swelled and pushed up slab cracking it so piers wouldn't fix problem).,
Second time with Olshan was for warranty work they didn't stand behind at mom's house. They were cheaper than other bid (small house that was being sold) so went with them. In middle of the project they said we needed more piers than originally estimated and wouldn't continue the job unless we agreed to pay.
Bottom line, hire an engineer to assess the problem and design a solution and then a foundation company (not Olshan) to follow the engineer's plan.
Good luck.