I have sole custody of me grandson and have had it since he was 6 months he is now 5 years old. His mother has never had any interest in him during this time as she moved from nys to Florida married a man who never met the child then had a child with him she shows up occasionally (very rarely) has since moved to Germany (husband in the army) is pregnant with her 3rd child and now wants to leave her husband in Germany bring her other 2 children to nys and try to get the child I have custody of. Help I have no idea where to go with this for advice as she never had an interest in the child prior and her contact with him is almost non existent

You say you have sole custody. Was that done through the court in New York? If so, she will have to go to court to get custody back. She would have to tell the judge why she has been gone this long and why it is in the child's best interest to go back with her. This is after all about the child. You would then tell the judge why you think it best that the child remain with you. If this custody has not been established through the court then she has the right to get her child (though after this long I hope you have gone to court). While you do not have to have a lawyer to go handle this, if she has one you should too.

I have no idea where to go with this for advice

You go to a local Family Law attorney. Such a person can best advise you how to prepare for a custody battle. I'm assuming that you were awarded custody by a court.

But people change. Your daughter is now married with 2 children. She has probably matured beyond the messed up person she apparently was when she had your grandson. There are a lot of factors here, your age, the financial status of both of you, your bond with your grandson and many more things, that a court will consider. So its not impossible that a court will return custody to her. That's why you need to prepare properly.

While its true that courts are generally charged with looking after the best interests of the child, they have traditional ruled for biological parents. But there are many factors that a court considers in determining what the best interests of the child are. Again, that's why you need an attorney to properly prepare your case.