Hi OP,
I felt very sad reading all your posts, they took me back to a relatively recent time when things were just as bad as you describe. Thank god things are different now...
Dsd, 12 when we met, was like your teen dsds, sullen,rude, would only address her dad, etc.
dss, then 9, would for years start every sentence with "dad", like a robot, we could all tell that even "dad" found it infuriating.
Like yours, dsc also came for dinner twice a week and eow.
Fortunately, my ds,then 11, had none of these awful issues and dh had a stress free time when dsc weren't here (that of course made me madder and dh less inclined to act...).
One day, after about 2 or so years, I couldn't take it anymore and forced dh to make my life better. As Flatiron suggested, he included me deliberately in every concern they had, I.e showing him something of interest would be passed on to me too, if they had a question he would ask me my opinion first... He did this (and I would show great interest, of course) for as long as it took to get them to change their behaviour. After about a year they would come to me (more!) because they realized I was not a monster.
Unfortunately exw was v bitter (I wasnt ow) and filled her kids heads with all sorts of nonsense (dad spent more time with my ds, he spent money on us which was rightfully theirs! Etc).
I kept my cool around them, was always pleasant, but if I hadn't got dh to take control over the situation I doubt things would have changed.
Dsd, now 16, is a frequent happy visitor, and dss, nearly 13, has been living 50:50 here since April. I did have my doubts about his motives (often felt he had issues "sharing dad") but it's such a balanced situation now I feel we can deal with things as a team, and, dare I say, a family.