Citizenship status is not a consideration in establishing an obligation in the US.
The mother should contact her (US) state child support agency. Be patient but persistent. Good luck!
yes
yes you can get money from dominican republic
Yes, under the Hague Treaty.
I suggest that you contact your town's/province's child support agency. When you get an interview with them, bring all the papers relating to your child support: birth certificates, acknowledgments of paternity, court orders, payment records, etc. Be polite but persistent. Good luck!
Depends on where the order was issued. However, normally the answer is NO. Just because you have diplomatic immunity, you are not exempt to matters such as child support. The consulate will address the issue of child support also, he could in fact lose his posting. Go to Consular Affairs both US and Mexico.
I don't know why Americans have so much trouble with this fundamental principle: If you are living in another country, then you are subject to the laws of that country. That includes Family Law. It doesn't matter where you come from (even the USA) or where you're living. So, yes, if the child is a resident of Canada, it is subject to the rulings of a Canadian court. A Canadian judge can appoint a guardian for an American child living in Canada. The guardian may be Canadian; it may be an American resident in Canada. The main criteria is suitability, not nationality.
Your State's child support agency can do this.
If you're in the US, no, a child cannot sue his parent for child support (payment for child support is not due to the child).
To apply for child support in this situation, you would typically need to consult with a family law attorney or a child support agency in the country where you and your children reside. They can guide you through the process of initiating a child support case and provide information on any applicable international agreements or protocols between the United States and the United Kingdom that may facilitate the enforcement of child support orders across borders.
Canada, of course, is the absolute best in everything.