Do Brethren think they are the highest court in the land and therefore can disregard laws which dont suit them including family court law?
This is theological reference, not a reference to Courts of Law. The Brethren abide by the courts of the land and are taught to respect and obey Courts of Law and to abide by their rulings. The reference to the Highest Court in the Land is a biblical allusion which speaks of the power and ultimate judgment of God, whereby God is ultimately fair and just.