Child Support

I am in the midst of a custody dispute with my nephew's bio father. I have had joint conservatorship with his bio mom and dad with myself as the one with rights to primary custody. Dad has a history of domestic violence and alchohol abuse... however it is 5 years ago. The child is now 7 and I have had custody of him for almost four years. From age 7 months until 4 and half the bio dad had visitation rights but never chose to exercise them. At any rate, we had child support established three years ago. At that time, he was paying for two children with a previous marriage and to my nephew. At this point, one of those other children is now an adult and he no longer pays on him. I recently received a letter from the TX Att General asking if I would like my child support case to be reviewed. My child's bio father owns his own business and at one time it is believed that he placed his other children on the board of trustees for his business so that he could write off the child support. How do I make sure that he does not withhold the amount of money that he earns? I am afraid that he will misrepresent the truth. Also, if he pays on one less child, does that make is more likely that he will pay at a higher rate? Since we are in the midst of this suit, should I have the review done through the Att Gen or just wait until we go to court ourselves for the custody suit? He is also ordered to pay half of the medical support but is refusing to pay for half of the counseling that I have to take my nephew to during this stressful time. In our orders, it says that he is ordered to pay for medical, which includes psychological care. Does he have the right to deny payment for this? I am sorry for the novel.

Thank you to anyone who can provide any info to me. This site is a wonderful resource!