Gotcha on teenage son being a turd. Had an upleasant evening with DS15 last week. H took him to "run errands" at 8pm on a weeknight because I think he was afraid that I might kill him. DS survived another day and improved markedly. I have no idea what DH said to him other than perhaps "Son, never fcuk with a 9month pregnant woman!" I admire his ability to have such a close R with a kid who isn't biologically his. It is a rare gift.
Your W certainly has her moments when she shows a loving side. Do you ever make a point to acknowledge how hard it is to deal with someone else's kid, particularly a teenager and how much you appreciate it? Also, it doesn't hurt to correct DS in front of W.