Our oldest son, "Jim," has a history of turning his back on people-?

sounds to me as long as you have money to give you are family, if the well runs dry then it's time to dump you like trash. you need to see a lawyer and see if you would be considered for grandparents rights in court. since he was adopted i think you fall under the same rights as grandparents. It's time to cut your finincial strings with him, he is no longer a child and allowing him to use you is teaching him to live life using people. Good luck.