It's going to depend on what the original judgment says and also on any later modifications.
Oregon law provides child support for a "child attending school," which sounds like what your two younger siblings are going to be. There are certain qualifications: A child attending school must be: (1) 18 or older; (2) under the age of 21; (3) unmarried; (4) a student regularly attending school; (5) has not graduated or reached the date to stop attending classes; (6) has provided written notice of their intent to attend or continue to attend school; (7) the support rights have not been assigned to the state; (8) the child is making satisfactory academic progress as defined by the school that the child attends; and (9) the child has a course load that is no less than one-half of the load that is determined by the school to constitute full-time enrollment. Here's link to ORS 107.108, which is the statute I'm referring to: http://www.oregonlaws.org/ors/107.108
If the child support order was entered or modified under ORS 107.108 (or ORS chapter 25, 108, 109, 110, 125, 416, 419B or 419C), then the order may require either parent, or both of them, to provide for the support or maintenance of a child attending school. Notice I said "may." Your father really needs to sit down with a family law attorney who can go over the current support order and give him specific advice based on his particular facts. All I'm doing here is referencing the general law.
If the mother is using the support money to pay off her credit cards and car, the "child attending school" statute might actually help your father because of ORS 107.108(5) which says: "If a support order provides for the support or maintenance of a child attending school and the child qualifies as a child attending school, unless good cause is found for the distribution of the payment to be made in some other manner, support shall be distributed to the child if services are being provided under ORS 25.080 (Entity primarily responsible for support enforcement services) or shall be paid directly to the child if those services are not being provided." This means that the money doesn't go through Mom anymore and she cannot take it for her personal use.
Also, your father were to set up a higher education savings plan for the childs continued education (meaning a "a tax-advantaged account established by a parent on behalf of a child for the purpose of paying qualified higher education expenses of the child at eligible educational institutions"), then the court may order payment in accordance with the plan instead of ordering support that would otherwise be distributed or paid directly to the child.
Another thing that your father needs to know is that unmarried children between 18 and 21 years old are necessary parties that must be given notice of any proceeding to modify support.
Here are a couple of helpful links that provide additional information:
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If you are married and living outside of the home, it is not likely that you father will have to continue paying child support for you. He may still be obligated to pay for some school, but the resources provided earlier should help you track this down. It sounds like your father just needs to know what is going on. If you are not receiving money he is sending for your schooling, then he should no so that he can work on changing the situation. He would probably be well served to consult with an attorney about modifying his payments.
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