@PolkaSpace
For me it's about balance. When the steps are here we'll often do things together whether that's watching a film (they are glued to their phones when TV is on, but that's just teens and they are watching too), having supper, playing board games, or whatever. but OP has explained they eat together and if they plan an outing she goes along. It's not like she's like right step kids are here I'm hiding away the whole weekend.
@PolkaSpace
Actually I disagree. In her op she said they were all watching a film together but she was in the bath.
She also said she'll leave them watching Tv together and go and watch her TV programmes elsewhere.
She said that they spend "most of their time" in the living room and she's not interested in that.
It doesn't sound like the outings are frequent at all. So it's just mealtimes (which with teens tend to be a speedy affair IME). Presumably that's because op wants her supper too.
Like I said. Balance. I don't think OP needs to be spending all her time with them. But if the family is watching a film, going to another room to watch something different every time is a bit off.
FWIW, we take it in turns to pick things so everyone gets something they're vaguely interested it. Usually we get vetoes too. I've sat through things I'm not that fussed by. They've indulged me on trashy TV.
Nothing wrong with a bath. I have mine if the rugby is on as they're obsessed and I don't know the rules really.
BUT. If I vanished every time they were watching TV (as op says she does) I'd never see them at all.
I do also insist on non-TV related activities. Cards, games, cinema. They're teaching me their fave video game at the mo. We sometimes bake together. Etc.
Some things that jumped out from OPs posts:
"when SC come I use that as my me time"
"at weekend I'll make plans with friends or family"
"DH has been getting moody about this recently accusing me of not wanting to spend time with his children. In all honesty I don't?"
"There is nothing exciting or desirable about spending time with his children"
"I'm quite happy for them to be around because it means I'm free to do my own stuff"
*
"*Right now they are downstairs watching a film and I'm in a bubble bath drinking wine and eating chocolate and it's bliss"
To me: that sounds as if the balance is gone and OP is actively avoiding them. I can understand why her DH is trying to address this.
I SO think her DH needs to spend more time doing housework and looking after their shared child, so that OP gets downtime in the week too. BUT OP says she doesn't want that, as she'd rather have her me time when the SCs are there.
I do (sort of) get it - I am a stepparent to two teens and it can be difficult. It's different though because I really enjoy spending time with SDs even though their phones are maddening.
Balance is key, and here it seems like it's gone. There's very much an us and them vibe, and it reads like OP is actively avoiding them. Her DH has explained he's upset by it, but no one can force her to engage. In his shoes I'd be upset too.