I think what you are referring to is that the father has filed Exceptions to the Report and Recommendation of the Master for Domestic Relations. He had a hearing before the Master, and was unhappy with the outcome, so he is essentially appealing the finding to the Circuit Court. If that is in fact what is happening, don't worry. In my experience, Masters' findings are upheld by the Circuit Court about 95% of the time. Generally speaking, the Master had to be wrong as to his/her application of the law for the Circuit Court judge to reverse the Master, and that hardly ever happens. Also, if this is an Exceptions Hearing, the rules that govern the proceeding are very strict, and people representing themselves rarely follow them correctly. This may mean that his case will get dismissed on procedural grounds without a hearing. Among other things, he is generally required to purchase a transcript of the proceedings before the Master. This is an expensive proposition, and deters many people from following through on their Exceptions.
If he is represented by an attorney, you may want to hire one, also, to level the playing field. If his only argument(s) are that the Master should have allowed for a downward deviation in the Child Support Guidelines amount because he is supporting two other children who aren't biologically his, you are probably fine because the law is clear on that. He isn't entitled to a credit for that, and the Guidelines are presumptively correct under Maryland law, requiring the court to specifically find that it is in the best interests of the children to deviate upwards or downwards from them. Hope this helps!
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Your question is poorly worded and very difficult to understand. I don't know what you mean by "exemption". There is no such thing as an exemption to paying child support. The only case that I can think of in which a party may be immune to paying child support is when he or she is unemployed and is caring for a child OF THE PARTIES who is under two years of age. In that case, the court will not be able to find that such parent is voluntarily impoverished because he is not working. But such immunity is only temporary until the child reaches the age of two.
The fact that he has committed to caring for another woman's children is irrelevant to his duty to support his own children, so his defense on that additional basis is groundless.
Again, your question is very unclear. You should probably talk to an attorney in person for detailed advice regarding your case.