Taken from the skids perspective there must be many indisgressions stepmothers make with no idea. It is why I think it best to reduce these problems by moving into a dwelling that has not belonged to either partner before getting together. 

It is good that you can see the situation thru the SKs' eyes.  So often, we steppers are so wound up in our own pain, we cant see much else.

We didn't have quite the same situation as you. We were living in a different home and had the kids on weekends and summers.  When I read about the current mode of the kids moving back and forth during co-parenting, I wonder how that works.  We had such transition issues every weekend. I think BM dealt with it when they came back, too.  Ultimately, all 3 SKs moved in full time.  Things calmed down then, if you can believe that one house with 5 kids only 6 years apart can ever be calm.  Lol.

I wish I'd had the insight then to realize how the transition issues were affecting them.  Hindsight.

Little things that had a larger impact. I wonder how many more there are, and if we'll ever resolve them all?

I don't think we can ever really resolve them all because, frankly, we don't know them all (and some of them, only make sense to the step kids).

When my SD was 15, I learned a lot about how she really felt about me, and I had been in her life for 10 years at that point. Everything she had been told by BM were lies, but it set the tone for how she felt about me... and her dad. I honestly had no idea until she told us. I mean, I knew what BM was saying to people, I had no idea that she was saying it to her young daughter. SD never let on, until one weird weekend.

SD, at 16, once said, "Well, you know my dad better than I do". Yes, that was true. Because her parents divorced when she was young, and he only had her EOWE, and I lived with him full time, I knew her dad better than she did. Not my fault, but there is was and she resented me for it. I actually felt bad for her.

Sometimes, we just can't win and it's through no fault of our own. I don't always blame the step kids, though, it is hard for them.

I know exactly what you're describing because I've experienced it a lot lately. Almost 13 years since H and I met and over the past few years a long list of my many "offenses" have been brought to light every time the SDs get upset about something. Things that aren't inherently offensive, and mostly things that I've done in an attempt to make a nice home or create a memorable experience for everyone.

But my SD's perception of things has been totally different from mine and H's, mostly I suspect because a) I do pretty much everything exactly opposite of BM because we were very different people and b) BM somehow manages to twist everything I do or say into a direct personal attack on her and my SDs. 

I had no idea until a couple of years ago that this was their perception of me and my way of doing things. It has been shocking to say the least to discover just how much I've been vilified for doing things that are completely benign or even downright kind and generous. It's definitely jaded my outlook on step parenting in general and now my advice to newer stepparents tends to lean more towards 'do less, care less' because it just feels like I've wasted so much time, emotional energy, and money over the past 13 years. 

If people cannot communicate then misunderstanding and frustration can happen and things remain unresolved.

DH does not communicate well much of the time with SDs and has not encouraged them to communicate with me, or really anyone, about their needs, wants, feelings. So no discussion could ever take place. I could try my dammdest to help, to figure out what was wrong, to this day...I can hardly get an almost 15 yo to tell me what she wants from the grocery store. She won't ask for new needed clothing or shoes. I just eventually gave up. BM is extremely reticent in her actions too and I think the SDs have learned from her very well (she's a GUBM and DH is merely a stupid man).

And we did move into our own home. It helped for a while but really, I am the one who cleans more and takes care of things here, just like in the rental. It was also my down payment that got this house in the first place. So when OSD complained to DH that it felt more like my house she was right, and I told him so. And no way was I going to pretend things were his idea (yes, he did ask that). So again, communication is key. Instead of telling OSD the truth he shrugged her comment off.

I'm an SD and a SM. I remember being angry about my mom bringing someone new in who had such different mannerisms and ways of raising kids than she did. I remember missing when it was just "us" - my siblings, my mom, and I. I remember hating that I lost my "power" as the oldest child.

As an adult, and as a SP, I can see where my feelings were justified and misplaced. There were errors that my mom and SF made (like moving in my SF a month after they started dating). There were errors I made (using my SF as a scapegoat for things I didn't want to take responsibility for). However, at the time, I didn't have enough life experience and my brain wasn't fully cooked enough to have acted much differently on my own accord.

I bust parents' balls on here all the time because what kept me from totally giving in to my emotions related to my parents' divorce as a teenager was my mother keeping me on a short leash. She laid it out very plainly that my SF was an adult who helped pay for things, and she was the parent. What she said was gospel. I could feel however I wanted to feel, but I could express those feelings in healthy ways. I could journal, b**ch to my friends, punch a stuffed animal, scream into a pillow, etc. However, I was in deep sh*t if I took it out on my SF. I was in deep sh*t if I convinced my siblings to be a-holes to our SF. I was to show him more respect than I showed her, and she was true to her word.

My mom swung too far and became too focused on her marriage as time went on, to the detriment of my brother and sister. But, for the "golden years" she was stable, I learned a lot about how to be a good SP and what to expect from a partner. I also watched where my mom and dad both effed up royally, and I have watched how that has hurt my siblings over the years.

I'm not saying that SKs can't be evil and mean. I'm not saying that they aren't ill-intentioned at times. What I AM saying is that parents need to own up that they nuked the stability that their kids had and need to find out FAST how to provide that again. That means different things for different families. I can't fault a kid for feeling very put-out when the home they grew up in 100% of the time now becomes their part-time residence and everything but the structure starts changing. Moving is one of the most stressful events a person can go through, so imagine the stress of "moving" between homes EOW while the physical home you know is changing in decor, food, atmosphere, etc. The kicker, though, is that SKs don't get that relief that comes with moving. They're stuck still seeing the remnants of a family and life that were all they knew, and watching as it slowly gets stripped away and their parent and the new partner don't want anything "old" to stay.

Basically, I see both sides. Kids and SPs get punished for the errors of the parents. That's why wet noodle Disney parents drive me nuts. I don't fault SPs for wanting to put their foot down, but they need to direct their frustration toward their partner. Their partner HAS to be in the middle. They HAVE to translate what their kids need into a compromise. Yeah, as the parent, they're likely going to lose out in those fights because what they win is a peaceful home with BOTH their partner and kids. And I lose my everloving mind when parents act like selfish d*ckheads who don't realize that they are already winning just by the virtue of being able to end a bad relationship, start a good one, and have their kids. Having to actually parent your kids and navigate them through divorce and a new relationship is the price for that, and not nearly enough seem to have to pay it.