I am the custodial parent of two boys 14 and 16. My ex husband…

I am the custodial parent of two boys 14 and 16. My ex husband has just sold his business at a value of just under 900k. He also has several properties - his net asset worth is approximately 2million plus the 900k cash for the recently sold business.
He and his new wife have decided to take 6months off, then buy and sell, do up property. So currently their status is unemployed. And so childsupport is now the minimum ($15 per week per child).
They have investment companies and a trust.
Several IRD admin reviews have repeatedly found his childsupport to be low, due to accounting which assessed his income to be 60k or less on occasions. This has been ongoing for approximately 8 years.

I am applying for another admin review, and if the same result is assessed, will take it to court.

Questions; in previous cases are years of child support minimisation taken into account (I am assuming that the sale and purchase agreement will reflect a real income in excess of $60k, that his cash sale of the business, with channeling of funds to both my ex's mother and new wife to minimise his nett worth, and several investments) taken into account for a court decision? I am certain from past experience that he will ensure there is no 'cash' assets, that it will all be invested in land or bricks and mortar, or transferred to others who are dummy directors or shareholders on paper.
Also can you recommend any law firms that specialise in child support hearings where family trusts, investments etc are set up to avoid child support?
If the court finds that in fact the last 8 years of child support has been below that which he should have paid, can this be rectified by a lump sum payment? And despite his current status of 'unemployed' can a current assessment of lifestyle etc be assessed in the court? If you have case studies to refer to that would be helpful.

Many thanks,
J.