Honestly it sounds like you need separate space - maybe like a little cabin at the back of the house or something - a Step den to go to.
If your in the house and they are acting up its gonna piss you off
Personally my only engagement would be to take things off them like the soccer ball
Maybe enroll your partner in parenting classes to improve his skills

I know that myself and my partner can't live together for long periods due to kids
My house is being fixed up at moment so I am living with himself and the skids for one month
We are three weeks in today and laundry stuff has slowly been bugging me - his two still wet the bed and then cause they are getting older and embarrassed they hide it
Today his daughter hid her dirty underwear in some recently washed towels and sheets and her bottoms in clean clothes
I absolutely flipped the lid
Normally I am disengaged fine and if they annoy me I go home- this actually helps to make them behave as partner wants me around and good behavior is key to this
But yeh today I really loss the plot- dirty people with learned helplessness - the great curse of a step kid

You need a place that is all yours for solitude. It helps you disengage and helps you relax and take a break for yourself

I tried to disengage when it was 50/50, but then BM got tired of SS12's attitude about wanting to live with Dad and kicked him out of the house a few months ago. Now he's my problem 100% of the time, and there is nothing I can do about it. I HAD to wake up and say..." OK. We are going to keep the house clean, the toilet seat DOWN," etc. I figure....What do I have to lose? If he gets to choose where he lives (according to BM), maybe he'll decide to live with her.

Yes, you can disengage but I found knowing what my absolutes were (clean kitchen, living/shared spaces and my furniture/personal items) were 100% engaged. I made sure DP knew this and everything else was up to him and do not engage on hygiene, their rooms/bath, food, etc.

I don't think it's possible, honestly. Or it wasn't for me, anyway. I can't just turn a blind eye to skid-related bullshit when it's going on right in front of me.

I don't advocate it for everybody who's dealing with stepkids, but separating from my ex, leaving his three shit-head snowflakes behind, was the only way I could truly disengage from their nonstop aggravating crap. I couldn't live with it, so out the door my two kids and I went this past June.

But no, during the three years I lived in that house with my ex and his kids, I never could completely disengage and not be bothered by the things they did. For me, it just wasn't possible, even after starting to take two different prescription medications to keep from losing my fucking mind.

So don't ignore it. Address the behaviors.

- No chores... no food. Feed them only after they have completed their reasonable chores for the day or anything you have asked them to do. Lather, rinse, repeat.

- Soccer in the house... soccer ball meet chef's knife. No more soccer anywhere. Again, lather, rinse repeat.

Any infraction, address it immediately with a notable consequence.

Don't get pissed, stay calm and enjoy applying the consequences. DH can either step up and parent before you have to or... he can STFU and have your back. Don't give him a choice.