The Child Support Guidelines are a presumptive amount that you must pay in child support. In order to pay less, you have the burden of proof of proving why you should pay less in child support. Additionally, to file a modification of custody, you need to show a material and substantial change in circumstances that would warrant a change in custody. I would highly recommend you speak with an attorney who specializes in Family Law to determine how to proceed. Good luck!
NOTE: This answer is for educational purposes only. By using or participating in this site you understand that there is no attorney client privilege between you and the attorney responding. This site should not be used as a substitute for competent legal advice from a licensed professional attorney in your area who regularly practices in the subject matter which your question is about. You should develop an attorney client relationship with the lawyer of your choice so that your communications will be subject to the attorney client privilege and have the other benefits of a professional relationship. The law changes frequently and varies from jurisdiction to jurisdiction. The information and materials provided are general in nature, and may not apply to a specific matter as partially described in the question
I think some judges do not look with favor upon litigants who file claims involving custody of children in order to leverage for something else. You know, pawns and all that. I assume that you have a greater income than you had the last time child support was set - and that is why you believe you will end up paying more. Otherwise, it doesn't make sense. And if you make more maybe you should be able to pay more. Or, maybe you ran the numbers incorrectly and should re-do it.
Bad idea. First of all the issue of "custody" doesn't apply at their age. It goes to primary residence. Second, the child support guidelines do not apply after 18. The child support statute regarding emancipation does apply.
To properly review your situation, more facts are necessary. For example, are you covering any of the costs for the children such as college? Is there a potential in your future for an alimony order?
You need an experienced lawyer to look over your current order (agreement) and discuss the current state of the law to uncover any unknown pitfalls and properly prepare strategy.
I would strongly recommend a consultation.
Sign up to receive a 3-part series of useful information and advice about child custody law.