Ledkr, I do think it's sad, and I want to see OP find ways to get through it that make the whole family stronger. I do feel for the kids - but I also feel for the OP. (I also don't think that her "being nicer" or buying gifts for the kids and overlooking their behaviour is the right way to create a healthy family unit, so I think she's been given some duff advice - but that's another point.) I think she's hurting. She's had a radical change in her living circumstances, one that while it may have always been a possibility, was not 'what she signed up for'. In theory, we all know that an accident for our DH could turn us into a carer overnight, or that we could lose our job and our home, or that our aging parent could end up needing to move in with us. But when any of those things happen, it can be catastrophic and stressful and extremely unpleasant - especially if one is not given much power to handle the fall-out! Imagine an OP writing to say that her MIL has had to move in, that she is difficult and moody, and that the DH won't speak to her about her behaviour. There will be those who say, "well, it's your husband's mother, suck it up", as well as those who say "well, MIL's are awful, what do you expect, change your attitude", and also those who say "poor you, that must be awful, she sounds a right pain in the ass - let's find some strategies to help you cope! And by the way, what the hell is your DH doing about it?"
OF COURSE kids are different and OF COURSE the father's responsibility is absolute - - but I can't fault the OP for being upset about it and having feelings about it....feelings which any one of us is capable of.
If she feels 'hate' and resentment, what would you have her do about it? I'd be the first to say that - for the sake of everyone in that family - she needs to find ways to manage those feelings. And she needs to consider her actions towards vulnerable children. But she's not wrong to feel as she does, any more than a poster who hates her demanding, hostile, bitter MIL on another board.
Ranting and venting is good. As stepmums, we often don't have anyone 'IRL' who will listen to us, or have the first inkling of what we're coping with at home. Even good friends aren't always helpful...I don't know ONE other person 'IRL' who is in my situation - my DH's sister was once, though, and she is a fantastic support to me - but she lives far away, I see her twice a year, and then - she's my DH's sister, so I can't always rant to her! There is a higher rate of depression amongst stepmums than non-stepmums - I truly believe that the isolation and the sense of constant judgement and shifting goalposts contribute greatly to that. These are support boards...support. That's what the OP needs. Good advice about how to change the dynamic that is making her so miserable. I think the fact that she's here, asking us all for help, is a clear sign that she's not unwilling to learn/adapt...but she also, quite rightly, feels put upon and angry with her DH.
We've never had a holiday alone or even a weekend, we don't get lie ins or peaceful meals together or the house to ourselves.
See, I don't think that is the "natural" or "normal" way to be and that a person is wrong to object to that situation! Don't misunderstand me - I am not saying that you are "abnormal" or putting you down for it. But my DH and I don't live that way, and wouldn't, and that doesn't make us "abnormal" either. We've had trips and weekends away (as we have a toddler as well as the teens, not as many of those as I'd like...), we have 'date nights' where we eat a meal separately from the kids and they're told to leave us to it. We have absolutely no family here and are pretty broke - so we do struggle a bit with childcare - we aren't able to go out as much as we'd like, and we need to make date nights at home or just share a beer in the garden, instead of dinner and the cinema or drinks in a pub!