Responsibility of ex husband to contribute to son's college education in PA?

Step father has been only financial supporter thus far for son's.car, food, apartment to help attend college in Chicago Illinois. Mother was sent letter of emancipation of daughter turning 18 yrs old as mandated in settlement by mediator: 1,600.00 per month. will cease, informed support has now ended. Biological father's income compensation 2013: approx. 900,000.00 bank president. Step father: doctor. Mother has had sole custody lives in Illinois. Remarried to doctor. What can be done to help son finish college ? And daughter will need 20,000.00 and car to attend cosmetology school. From quick books account mother can account for every penny spent from child support.