In my experience septic rules are very strict and vary widely upon location. I would first go to the local agency in charge of septic tanks in your area and see what is required and what can be done before coming up with a plan about what to do in your situation. By changing something with your system that might not be allowable, you are opening up yourself to fines and lots of trouble when you go to selling your house.
I highly second the bolded part. I live in a town where many things do not require a permit and even fewer require inspection. But septic work here? You'll need a plan (more than likely from a licensed person), a permit, and inspections along the way.
That is the right way here to deal with changes, reality is the AHJ is one person once a week and with larger lots there isn't much to see just driving by.
Here is my two cents.
Such a new system, absent abuse, should not have failed. Multiple failures in the development seems to point to either a problem with design or installation. After 5 years and a change in ownership, I would be surprised if you have any recourse against the builder/designer/installer. As suggested getting the plans from the AHJ isn't a bad idea.
If terralifting actually happened a year ago and needs to be done again, I would not have much confidence that a second round will be successful.
All of the work you ask about seems like re-engineering the existing field on the fly. And without identifying the cause of the problem I would not be inclined to reuse most existing materials, that might change depending on what type of system it is.
I would call out an engineer, not a septic company (here there are independent engineers and you can then bid out their design). In my experience they'll look at existing soil conditions and design a system for well less than a grand -though it has been about 10 years since I hired one-.
Here land is somewhat plentiful and the prepared option for a failed leach field is abandonment in place and replacement if a new location. IIRC that is in part because removed leach field soils have to be disposed of in certain manners.