Should support be stopped if child turned 18 and is attending an online school instead of a traditional school?

My grandson was living with his dad and step mom. It was a nasty divorce and the parents do not speak. The step mother takes over all court matters. My grandson got into it with his step mom. His dad gave custody back to his ex-wife. My grandson was diagnosed with PTSS and has had problems in school. He got behind so his mom let him enroll in a charter school online. Now the dad refuses to support him because he is not in a traditional public school and he turned 18. I am really upset because my grandson is doing so much better in an online school. But without enough support there will be obvious issues. Not only that, FOC in the county automatically did it with no regard to the mom's input. The 18 year old is a victim of a nasty divorce and should not be. He is struggling to understand why his dad had not contacted him in over a year. They live one hour from each other. The oldest son is being supported - new truck and a senior at MSU - paid for by dad and step mom. Can I please have your words of wisdom?