Yes - but only if your DH is able to set boundaries on the ex and the kid(s) and prevent that drama from infiltrating your home. In your case, he is totally incapable of doing that.  Disengaging is not the cure for you - your DH needs to get some help so he can stand up for himself and you. 

I've disengaged for the last 2+ years from my H's 27 year old daughter and I am living my best life. I was happy regardless but so much better now that I removed such toxic energy from my life. H is not a Disney dad and he supports me 110%. He doesn't tolerate anyone disrespecting me/us, our marriage and his daughter is no exception. He has my back and that makes things so much easier.

Disengagement has been a blessing. I wouldn't have it any other way

Your DH is not support your disengagement,  If you don't do it he happily does it.  You get a better life out of disengagement.  You don't have to worry about doing anything for SD or stepping on her toes.  She out of sight out of mind 

Honestly, I dabbled in it for several months and it just made my life more difficult. Disengaging with step kids meant I was disengaged from my DH while skids were around....which is half the time. And in disengaging with skids and dh I felt I was disengaging from my entire life including my own 3 kids and our shared child.......

And I learned that disengaging isn't really what I want....I just wanted my DH to step up and grow a pair and lay down some rules/boundaries and STICK to them with skids and BM. But no...

I understand the idea behind disengaging but it doesn't seem to work in all instances. It depends what both people's expectations are. I personally think that if a child is in my home then I have the right to have my own personal house rules and also give commands and receive respect from the child as a family member and adult. When I take care of my godson I give him commands and tell him things I want done, I correct him if his tone feels disrespectful etc. What I don't do is make decisions regarding his schooling, food choices, activities things like that. That's fine with me as I am paid to care for him. Now as a stepparent if I am expected to do even more than I do for my 10 year old godson I need to have full decision making power for how they are raised because this is affecting my life in a more serious way and they will be in my home. If the bio parents cannot also come to agreements with me on how the child is raised (ie: diet, medical decisions, schooling) then we will not be parenting together which includes cooking for, cleaning up after, chauffeuring, teaching, grooming etc. If I do these parenting-like labor activities then I will be compensated like I am for my godson because that's called babysitting not parenting.

Here's a positive story for you:

I kicked DH and Killjoy out of my house.  And I lived happily ever after.  The End.

For me.

In the beginning...5.5 years ago...

DH was separated from his ex, and we had then-SD15, and Then-SD8.5, and a Toxic Troll BM, who looked for reasons to yell and cuss out dH. I was underemployee and new to all this step family stuff, and have no bios to escape with. Eldest SD was rude to me and dirty and there were screaming matches every morning before school. Younger SD was sweet and kind.

Then...Enter disengagement...1.5 years into this game..

DH divorced, all the tussel involved was gotten through, we could breathe, because as you know the fear of the unknown was greater than the pain of the actual. Eldest SD, now nicknamed Winona, because she was caught stealing from a shop at the mall, was being rude and horrible. Causing many arguments between then SO and I. I found this site and learned all I could about disengagement. Once I did, things were easier. Winona stayed in her room mostly. It was hi and goodbye and not much else. The normal acting like I did not exist, etc. I got better employment year by year. A weight lifted.

2.5 years ago, or so, SDnow20 graduated high school, had just turned 18, had just been beaten up by Toxic Troll. She ghosts us for a while, is working, and living somewhere else. A few texts to DH, but no meetings for dinner or anything. MY employment gets better. Munchkin SD youngest is still sweet. Our bond has grown. Toxic Troll has been in and out of abusive and horrible relationships. Taken out restraining orders, been regularly abusive towards DH. Is still Toxic towards me  (yes we got married 1.5 years ago!!!!).

Now: I have a wonderful new job. SD13 munchkin is sweet and smart and really excited about life - getting a job, a license a car.

We bought a house.

SD20 has no job, no license, no life. Her and Toxic Troll fight all the time. SD20 Feral has become a Forger - of checks! She has stolen from Toxic Troll and possibly others and cashed them against multiple bank accounts. We are no contact and very much disengaged. She has asked to live with us. Hard no. Life is awesome!!! Disengagment is awesome!

Thats my happy story.

I have a very positive Blended Family experience. But... I have never disengaged.  I chose to be all in when my bride agreed to marry me.  So I have been all in from day one.

I raised SS-27 as my own since his mom and I married the week before he turned 2yo.  As equity life partners we are equity parents to any children in our our home regardless of kid biology. As it turned out, SS is an only child in our family.

He asked me to adopt him when he was 22 and we made that happen.

We are very proud of the man we raised together.  He is a man of character and standing in his profession.  He lives a great life.

All it took... was commitment, partnership and zero tolerance for any behavioral bullshit from the kid and total confrontation and destruction of the toxic blended family opposition (The SpermClan) when they pulled their manipulative crap.  They are now far in our past and for the most part far in our son's past.   He does maintain contact with them.  They make no effort to maintain contact with him other than to try to manipulate money out of him periodically.  The guilt trip over helping to finance the raising of his three also out of wedlock Spermidiot spawned half sibs by to other baby mamas is a thing that they try periodically.  Now that the  youngest is 18 I doubt that there will be many more attempts to get money out of him but.... with these idiots you can never know.

We celebrated our 25th anniversary this past summer and will be having Thanks Giving together in Europe next week when we go to visit our son.

.. but it took a lot of wrangling and grief and one near-hysterical blowup on my part to get here. We still have occasional disputes, but they are far milder than they used to be. I'm not totally disengaged--just mostly. DH gets all butt-hurt when I indicate that yes, I am still withdrawn and no, I do not intend to change that.

I wish I could tell you it's easy, but it's not. DH and his spawn have infuriated me a good bit, and I have had to set a lot of boundaries and then constantly patrol and enforce them. Shock of shocks--I have also had to do a good deal of examination and adjustment of my own behavior. (As a recovering Catholic, this is second nature to me.) There were a lot of sometimes heated discussions along the way, and I have put more effort into achieving peace than I would have preferred.

It can be done, but is not for the faint of heart.