If the 13 year old will talk politics he isn’t shutting you off. I do realise politics is not an easy area if you differ a lot, but it does mean he is still communicating. Can you at least quietly grit your teeth and hear him out?
The 16 year old will see himself as a young adult now... think back, I know I did and expect you did too - so he is probably more interested in relationships with his peers and the car and so on than family. I think that’s natural. I think if you keep the door open he’ll come back, in time.