Partner isn't interested in my kids HELP!!!

Hi,

I'm in need of some advice.

I have been with my partner for 2 and a half years, I live with her and her two kids girl 7 and boy 10, I get on really well with her kids, its a good relationship and my kids get on with hers, however very early on my partner struggled at times to move on with me after her divorce, I was very patient and didn't rush her. (her relationship had ended 2 years before we started)

The issue now is she now pregnant with my child and that will be here in feb next year, the issue is when my kids are around on a weekend, the mood is horrible in the house, I mean she's civil with the kids but when they are around, she cleans, cooks, goes out, does anything to avoid been around them, she does try but by her attitude I can see she's not comfortable around them.
She said in the past that she was unwilling to bring another family into this house, we talked and I thought we had moved past it, but nearly a year on the atmosphere when my kids are here is the same.
I will state my kids are normally well behaved but do have there moment like most kids, she sometimes says that my daughter is a little rude to her interns of hello's and bye, but in the same breath I don't think my kids know how to communicate with her has she hasn't really tried and I know my kids feel like guest here as they have said, my kids are 6 and 12.

Another thing that really spooks me is that she is still very close to her ex's family which I don't mind they were in her life a long time, but she makes no attempt to get close to mine.

She still has family day on a sunday with her family we are not included in that, nor will be ever as she see's it as her time with her family, but for me are we not building a family together now!!!

I really need some help with this as I just cant see how this can last and I feel like I'm letting my kids down, I thought I'd found the perfect partner, I'm not expecting her to be a mum in any way, but I see them once a week and I want them to enjoy it and feel comfortable when they are here, maybe they dont pick up on it yet, but she just goes so quiet when they are here and if they are noisy or do something silly I'm litterally waiting for her to have a go at me for it in some way.

Its hard to decribe but she is just so very cold when they are around, its just something I can feel, i try to be so nice as in the past when i mention it she flips and goes in a mood without any explanation with regards to her feelings, all I want to do is for her to be honest with me so we can address the problem, but I've waited long enough.
I need to do something now as leaving it alone hasn't and is never going to work.

Any advice would be great. thank you

maybe need more time nd more patient.