Disengaging is not a one size fits all - you craft it to suit your own particular circumstances.  Having said that, there are some general principles - this article mainly addresses SKIDs who are still living with parents https://blendedfamilyfrappe.com/disengaging-essay

Yours sound older.  I disengaged when my SDs were 6 and 8 and remain disengaged to this day - they are now mid 20s.  The form it takes with me now is that I don't go to SKID events - eg I didn't go to SD25's graduation - but if either of them got married I would go to that.  I don't go along usually when DH sees them for lunch etc.  However we recently moved and they both came over for the day a couple of weeks ago.  This only happens occasionally.  Relations have improved in recent years but I still hold them at arm's length.  

At times I want a divorce.. because I am miserable. But,  the thought of his kids getting everything we worked for drives me crazy.

If you really are miserable and want a divorce, make sure that YOU get what you have worked for, if you decide to go that route. No reason his kids should get what's yours.

Otherwise, when the thought pops into your head to ask about them, pause and remind yourself how you will feel afterwards. Remind yourself that you really don't care how they are.

Disengagement can work but you also have to find a way to let go of the hurt. Hanging on to it means that it matters to you. What you want, is complete indifference. Not easy, but possible.

What is your husband's relationship like with his kids?

If you feel like the 2nd wife, 2nd life, your husband bears some responsibility for that.

Asking about the skids and then getting upset just feeds the anger.  It is a vicious circle and it keeps getting worse.  The only solution is to stop.  I get that it is hard because that righteous anger actually feels good sometimes.  It is like a release valve venting all of that pent-up hurt and fury and frustration.  But it doesn't solve anything and it just makes things with your DH worse in the long run.

If you are truly done with your skids, be done with them.  When you find yourself starting to ask about them, find a way to stop.  Literally tell yourself "STOP!!!!!"  Excuse yourself to the bathroom, dig your nails into your palms, go get a glass of wine, sing a song in your head....whatever you need to do.  Just find a way not to mention them.  Eventually it will get easier.  I get the argument that you want to be "forewarned about what might be coming."  That was what I used to tell myself as an excuse for why I had to keep picking at the scab and keeping the wounds open.  It was crap.  Once I finally stopped letting them live in my head, I was much happier and the "emergencies" that I did hear about from DH were much easier to let him deal with since they were his problem with his children.  Not mine.  

You can let go if you want to.  

For me, disengaging took some practice, and it still takes some work. It's pretty normal, I think, to want to ask about your partner's interests -- his work, favorite sports teams and hobbies, his kids. You have to train yourself not to ask. Redirect your own brain and activity. Lots of self talk. And be patient with yourself. When you recognize that you'd normally ask about his kids, redirect that thought to your pet, or the neighbor, or a recipe, or the new shoes you'd like to buy. You'll get the hang of it and over time it gets easier.

My DH has recognized that I stopped asking about his kids. Sometimes it makes him sad. But I don't stop HIM from talking about them. Usually it's just a report on a grandkid activity, or a job situation, or something. I keep my responses superficial and I can usually find something nice to say, but eventually it will end in "uh huh, how about we cook the steak for dinner tonight?" Every now and then DH wants to have a deeper discussion about them, and I do engage in that. Because it's for DH. But he knows that I'll be honest about my opinions, which is sometimes hard for him to hear. But if he asks, he'll get what he asked for.