I'm sorry to hear of your family's dilemma.
Thank you for the additional information. The mother, of course, is entitled to custody or visitation with her child. The DNA test done by the other man will not hold up in court. He will have to petition the court for a Determination of Paternity, have another DNA test done by an approved lab, and then if he turns out to be the father, the court will grant him parental rights. The court will not award custody to the guy's mother though.
Your son, if he thinks that he may be the father and not the other person, needs to have a DNA test done as well. Because if he is not the father, he will have no parental rights under the law, and the real father will be able to have visitation. The real father will also have to pay child support.
I'm afraid that it is going to cost a lot more than $500 to get an attorney to represent your son. In fact the court ordered DNA test alone is generally more than $1,000. I would suggest that your son take an inexpensive DNA test now, and if it does not show him to be the father, he may want to reconsider fighting in court with this other person---as there is a good chance then that they are the true biological father.
Your son's girlfriend will almost certainly get primary custody of her child and if the other guy is the father he will only get some visitation---so as long as your son continues to live with his girlfriend he will be able to continue raising your grandchild.
I wish you and your family the best in 2011.
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