A lot can be changed by your DH. He can tell his kids that they are to speak to you with respect or he'll take them to task over it. However, in this situations the DF is often caught between a rock and a hard place with the kids and ex-wife, so he may shy away from this, or not have the balls or whatever.
I wouldn't disengage. I would just have your own boundaries. Read 'how to talk to teenagers' and use the very simple method of never offering any opinion (you a both wrong and stupid!), just eliciting information and then making neutral comments (really? gosh. what did you think of that, or just go 'oh' interestedly). When they are rude to you, don't reply just remove yourself (I usually said 'how rude' and stalked out) and wait for them to need something, food, lift, whatever, then say, I'm not doing anything until I have an apology for the rude way you spoke to me. Take any old apology, even a rude one. Move on. Be kind to them, make them nice food, tell them nice things about themselves (i will say, I find this last one very hard but it does work even if you are just saying 'wow you know much more about politics than I did at your age' even if it isn't true. They have to warm to you.
Don't do anything for them if they have something outstanding. If they haven't done x or y say I will start making dinner when you have done x. I will give you a lift when you've done y. Welcome to transactional parenting - everything is currency.
When you have them in a quiet moment try to tell them as honestly as you can how much it upsets you when they speak disrespectfully to you and that your DD hears someone speaking to her mother like that.
I realise all this is much easier to say. I am six years in (12 to 18) and the rudeness has tailed off. But even now if he's rude I bristle and the conversation ends.