-In your shoes op I think I would really double down on the course enrolment. Go to the college with him if possible and fill out the papers there and then. He may be more amenable to this than you think when he realises that the majority of his friends will be doing something in September. Drop in the names of his friends occasionally and ask what they are doing.
-can you and your dh make an effort to present a united front? I know it’s far from easy when you disagree! But don’t let your ds play each of you off against one another. Your dh should come down hard on him if your ds is aggressive towards you.
-I wouldn’t be attempting to take a phone off a 16 year old either. He should be capable of exercising self control over its use by now. Parenting should now be altered from “top down” to “along side”. In other words, he takes responsibility and makes his own decisions. And you support, believe in him and expect him to make the right choices, even if you don’t quite yet 😄. He is young, he won’t get it right until he feels the full consequences and learns for himself. Give him more responsibility not less.
-Maybe time to dress up and take him out to a restaurant lunch one on one where he doesn’t feel 100% comfortable 😆 and ask him about where he sees his life going? What is his plan for the next five years? What does he enjoy? How does he see his life panning out?
-At the same time you would maybe have a quiet word and tell him that his siblings are looking up to him and watching how he behaves?
-And don’t forget to keep having good times with him even if you have to grit your teeth. Even 10 minutes a day is better than nothing. Use humour and junk food. Start each day with a clean sheet. Ultimately it’s his relationship with you and your dh which will keeps him safe during the cocky know it all stage.
-Step back, live your life, and let your ds get on with his, don’t micro-manage or take the tetchiness personally. He does his own washing and chores. Cleans his own room. It’s up to your ds now and you can support and steer from the sidelines and approach him with a “it will be interesting to see what decisions you make for yourself for September; your dad and I know you are more than capable of making a success of whatever you put your mind to doing”. I know it’s awkward and a bit cheesy but they need to hear it!