This is my first post on here.....!
I am at my wits end....... First I will set the scene.

3 teenage SD's aged 13, 15, and 18.
I have been with my other half for just over 2 years. We were both cheated on and left by our former spouses, the relationship between the 2 of us in incredible, it's very different with the girls. He is a wonderful man (he has his faults!!! But on the whole he is wonderful).
His ex had an affair and left him, 4 years ago (for a family member :jawdrop: ) and she then moved 150 miles away, leaving all 3 kids with my OH.
As well as being a Dad, he has a high-powered full time job, and runs his house.
The eldest doesn't see her mother, the other 2 do. It is supposedly every other weekend, but it is rarely that often.
I do not have any children.

My problem is that we are just in the process of buying a house, where all 5 of us will live together. And after the recent events, I am terrified.
I am at my wits end. I don’t know what more I can do now.
I have tried and tried to talk to him calmly, shout at him, get angry, nothing works.
I do not expect his kids to be angels, but I do expect respect and for them to behave appropriately.
EVERYTHING is always on their terms.
They disobey him, they treat and talk to him terribly, they have no respect for him, they are constantly asking for stuff and they are spoilt.
He has clearly allowed them to do what they want, when they want, and now we are, and will continue, to pay the price.
But anything they do that is really wrong, he always defends them, defends their behaviour, defends their verbal abuse, and defends their actions, even when they are 100% out of order.
I simply do not understand why he would do this?
Only once, he was nasty to me in front of them, they gang up against me, he undermines what I ask them to do.
I feel that it’s just unacceptable.

The kids are all very different, and have their own challenges, but none of them ever seem to get addressed.
The eldest, her room is a tip, she is 18. Why does she NEVER think that her Dad had 3 kids, a home, a full time job? Why can’t she ever get her lazy self out of bed, and think, I’ll do the housework, I’ll sweep the garden, I’ll empty the dishwasher.
She would NEVER EVER do anything, it’s hideous! She’s so extremely rude to him, she’s always aggressive and shouting at him.

The middle 15 year old, just wants to control everything, she is mouthy. She is also a bully. She cannot caveat every downright nasty thing she says by saying “I’m not being rude”.
She can never been asked anything, or told anything, without questioning everything, moaning, and getting the last word.
If you ask her not to do something, she just goes straight ahead and does it anyway.
The youngest, 13 year old, is very lazy, she is not trustworthy (she lies), she’s always asking for money/things, and she is incredibly rude.
I do not expect, or deserve to be treated the way I am treated by his children.
Being sworn out, being verbally abused, being told “they won’t support our marriage”, swearing, burping, and with no respect at all.
The worse thing is, I feel totally alone.
I feel it’s them against me.
We never go out alone when we have the kids. NEVER.
He has promised on numerous occasions that he would address the kids behavioural issues, he does for a while, then gives up.
I do think their mother causes problems, but this is something you should have dealt with, and I believe he should say to the kids, if their mother is jealous and nasty, that is her problem. They shouldn't ever feel they need to take that out on me, or him.
They can’t even tell her we are having a great holiday because she will get jealous (their words).
They shouldn't EVER have to pretend they are unhappy when they are on holiday with us, it is absolutely pathetic, and unfair to the kids.
She has left her kids for another man, but is forever all over social media “I miss my babies so much”. Clearly not enough!
Her and my OH had been split up 2 years when I showed up, yet she is vile to me, without any justification.
The kids have 13 weeks holiday from school, last year she had them for 2 weeks.
We can never book a holiday, because if he asks her to have them for a week, she will just say no.
She dictates when she has them, so we always have to fit around her! She had them for approx 50 nights the whole of last year.

He even lets the eldest and her bf sit there burping at each other. I find that totally disgusting.
In my opinion, he lets the kids get away with far too much.
They are spoilt, and it doesn’t get him anywhere!
Surely he is firstly their parent, not their mate?
It’s his house, and your rules should apply. (Oh I forgot, they don’t have any!!!!) There are no rules at all in his house! They don’t even have to put their washing out or bring their glasses down, because he’ll do it.
They never clear up after themselves, any of them.
I am forever being told "you can't tell me what to do, you're not my mother". They always want things their way, and on their timescales. "can you please clean up the flood you've left after you're shower" response "yes, once I've done my hair, done my make up and got dressed".
I will not then do it, my other half does.
he walks round their bedrooms picking up dirty laundry, cooks all their meals, cleans up after them.
He is an amazing Dad, he deals fantastically with their emotional needs and well being.
But he will do chores, rather than them for an easy life.
He cannot see that he is not helping them by doing EVERYTHING for them!
The sit on the sofa, and would never think about putting it back nicely.
I just cannot bear feeling like I have no support from him, and no respect from the kids.
They think they don’t have to listen to me, because he often says the opposite.
They all play you, even their mother.
It is absolutely mortifying
The kids blame any discipline their father dishes out on me.

I feel totally out of my depth her, sorry if this isn't very clear.

Any help or advise would be massively appreciated.

Thanks

Helen