I was not exactly in a similar position to you, as I disengaged pretty much from the outset - a year into my relationship with DH, when my SDs were 6 and 8.   They were only with us EOW and some time during holidays.  Their mother made it impossible for me to have a relationship with them, through her PAS.  

What I would say to you, is that it appears that you feel you must be a "better" stepmother because your DH is putting pressure on you to do so.  This is not his call, and you can't conjure up warm feelings towards your stepkids if they are just not there. I think you should stop adopting an apologetic attitude towards this, which comes across in your post. As long as you treat your stepkids with respect and courtesy, you honestly don't need to do anything more.  You don't have to "parent" them - their bios are their for that.  And besides they are teenagers.   I wouldn't have very warm feelings towards any relatives that came to stay, and left a mess in the house every time!   I think you are being too harsh on yourself. 

YOU define what a good stepmother is - there is no rule book. I was fortunate that my DH was a strong parent who didn't want my help parenting, and so I took on the "Fun Aunt" role - I'd throw the ball with SS (he's now 20), watch movies, play games, etc - but I like kids and I liked SS. DH did 100% of parenting, I helped here and there with things when needed, but DH never expected anything from me other than to respect his son and be kind to him, which fortunately, most of the time, wasn't hard.  If he needed my help with something, he asked and was grateful, he didn't expect it. 

As time went on, my SS was eventually alienated by his mother and his behavior became more and more challenging, though not directed at me - that was when I stepped back a lot and I have very little relationship with SS today. I'm polite and pleasant on the rare times I see him, and that is it.

You don't say how much time you have the kids - but I think what you are doing is fine.  As long as you are respectful and kind to them (provided they give you the same in return), that's all that's needed.  You don't have to care about SS's game, you can nod and say, "oh, that's nice!" like you would with a coworker you find boring. You aren't obligated to develop a deep relationship with your stepkids, which isn't likely anyway, given their ages.

BUT, your DH does need to temper his expectations and understand where you are coming from. You aren't a kid person and aren't ever going to feel the same way about his kids that he does. You aren't obligated to do anything for them and have every right to take off and do your own thing when they are around (in fact, I'd suggest it).  It really is fine to think of yourself as "Dad's Wife", not "stepmother".  I do.

This is all you need to do:  "To be quite honest, my motivation to be a good SM has been to be a good wife to my DH."

It can take some time to find a balance, disengagement is not the same for everybody.

I never set out to purposely disengage, but like you, I am child free by choice and have never been interested in being responsible for raising a kid. I did not care to be the World's Greatest Step Mom, in fact, have never really considered myself to be a step mom, as BM was and is, alive and well.

I feel that I treated my SD (now 29) ok. I did what I felt like doing for her and no more. I never felt obligated to do anything when it came to her. Sometimes I joined DH and her for a trip to the park, sometimes I didn't. Sometimes I bought her things, sometimes I didn't.

DH is the nurturing type and loves kids so he was a hands on parent when SD was here, he never expected me to take care of her. He never felt that it was my responsibility. That took the pressure off. I never felt that if I did something nice for her, or cooked for her, that I would be expected to do more, and more, and more. DH was glad for what I did do and that was that.

I did not disengage when it came to my home. SD's room was always spotless when she arrived and I expected it to be the same when she left (DH agreed and made her pick up and vacuum her room). I also expected her to clean up after herself in other areas of the house while she was here. Disengagement does NOT mean giving up your power or say in your own home.

DH will mention something that has irritated him about SS's behavior/irresponsibility, and I used to blurt out "then he should have consequences!" In those moments, I quickly realized that DH was just complaining and not necessarily asking for my input. So now I just swallow those would-be suggestions and nod very neutrally.

I think you may have swung in the wrong direction because of your husband's expectations and reactions. If he talks to you about his kids, you should be able to respond and not feel like you have to swallow your opinions. He should not expect you to feel the same about his kids that he does. This could be causing your coldness towards them.

Sometimes, a step parent resents their step kids because of their partner, not the kids, themselves.

A few things to ask yourself:

1) Are you actually becoming cold, or just not as warm as you think you should be? There is a difference between these two things, and the latter is directly related to how you perceive yourself and your own expectations of how you should behave.

2) Why have you conflated being a good SM with being a good wife? Would you say the same thing about being a good wife means being a good daughter-in-law or sister-in-law? Your SKs are in-laws, and just like you can have varying degrees of relationships with each in-law that isn't tied to how good of a wife you are (because those relationships are also complicated), the same can be applied to SKs.

3) What can your DH do to help you in this transition? I know you say this is "all you", but I see a few things your DH could do differently to help you transition, such as telling his kids to clean their rooms before they go and putting their dishes in the dishwasher without you having to ask/notice.

My personal opinion on this is that you've put too much pressure on yourself to try and fit in to the family dynamic that existed before you came along versus creating a new dynamic with your DH. You want to do everything to be a "good wife" without putting that same expectation on your DH. That's not me saying your DH is a bad husband. That's me saying that you expect better of yourself than you expect of others, which is probably a smart outlook on life except for when you combine your life with someone else.

It would likely do you some good to lower your expectations of yourself while raising your expectations of your DH. Disengagement is a great tool to help with this, but your DH needs to pull his weight, too, as I mentioned in the 3rd point. You might find that you care more about your SKs when your DH begins showing in a way you appreciate that he wants you all to integrate and develop a new normal versus you just slipping into a pre-determined mother-wife skin.

from another CFer! I'm so glad you posted.

 I've always felt that steplife is exta ultra uber challenging for a childfree person as it adds yet another layer to an already complex dynamic. CF people exist on a spectrum, ranging between thoses who can't tolerate kids at all to those who love them, but just don't want to be a parent. And some kids are great, while some are little sh!ts. So for a CF person, the situation has to have the right partner AND the right type of skids AND the right amount of exposure AND the right ... vibe? tone? As I said, complicated.

I assume your H knows you're CF, and did before you married? If so, he CHOSE you, knowing you weren't a kid person. You sound like a caring, intelligent woman, and need to let go of the guilt and any unrealistic expectations you may be putting on yourself. Don't twist yourself into a pretzel trying to be someone you're not. You are you, and absolutely fine just as you are! Quit thinking you are the problem, because you aren't. It's the SITUATION that is the problem - maybe it isn't the right one for you, maybe it is - but try turning the lens around and change your focus. 

Get brutally honest with yourself. Examine what doesn't feel right, what does, and what doesn't work for you. And let go of the whole SM thing. Just be your DH's wife. That's the relationship you should care about. Give this a try for a while, see how you feel, and be sure to factor in how COVID is magnifying a lot of issues. (((hugs)))