I dont have much advice but I want to empathize, 3 kids under 5!  That's a lot to handle!  I had a hard time accepting my 3 SKs but they were older than your SS.  I don't think any of us is cut out to be a SM, its hard.  I do want to mention one thing that happened with me.  When they were coming and going back to BM, that was the hardest time.  Once all 3 moved in full time (long story), i saw them differently.  I know that's the very last thing you want but just know you might feel differently if that were to happen.  The move in coincided with me going to counseling so maybe that was a factor.  Good luck, Stepemma.

Same here. SD is 10. Her behavior makes her just unpleasant to be around. Even DHs family agrees. She was supposed to do a "grandparents trip" last summer, but they cancelled on her due to her poor behavior. DH wasn't surprised. Wherever we go (grocery store, neighbor's house, trip, grandparents, etc) all she does is complain and mope around. She is inconsiderate and doesn't understand when things "don't go her way" or if the group wants to do something different. 

As she has gotten older, SD secludes herself in her room when she comes over. Obsessed with technology instead of hanging out with friends. Being a hermit doesn't help her poor behavior either. DH totally acknowledges it. They are polar opposites and sad to say but SD is a carbon copy of her BM. DH made a poor choice when picking her (acutally an accident) as her mother. 

Well - does your partner do the parenting when his son is there? If not, perhaps that's the place to start, with him taking over parenting the boy so you can focus on your girls.

This is a tough one, because like it or not, he's your girls' brother, and he'll always be part of your lives.  But definitely set limits on DH having him for more time unless he's going to step up majorly in the parenting department. 

I've found that it's near impossible to accept another person's child as part of your household if they do not operate under the same values that you have and that it's near impossible to impart your values on a child who is only with you EOWE or who operates under a completely different set of values in the other household. 

My SSs are whiny, lazy, dirty, entitled brats who expect to be catered to. DH doesn't want to be the heavy because he only sees them four days a month. For this reason, they will always be annoying houseguests to me. I think I've accepted that, but it doesn't make my life any easier. There's also the whole "pretending" to think theyr'e wonderful when other people are around, because any adult who finds a child annoying (unless that child is their own) is a demon in the eyes of outsiders. 

I feel this exact same way about my SD4. My husband and I just had an ours baby back in July and I don't want SD around my daughter at all because her behavior is so bad. My SD and I had a good bond when she was smaller but now I can't stand being around her. She is with us 5 days one week and 2 weeks the next and I dread those days and can't wait for her to go back to her mothers so I can enjoy my new baby with my husband. DH's family has made comments too about how I "leave out" SD because I don't post pictures of her on social media and only post pictures of my DD. I posted my baby for national daughters day and DH grandma commented saying "what about your other daughter?" I made it very clear to DH that sd4 is not mine and she's not gonna take away from me having my FIRST baby. I'm to the point as well that I don't think step life is for me. I'm tired of having my home invaded by a disrespectful brat who screams and hits and cusses.