Yes, when my SDs would come over, the topic of NPD BM would often be inserted into the conversation by them, particularly over the dinner table where they had a captive audience.  My DH would tend to acknowledge briefly but not ask for more information - I would just ignore all such references.  I don't think I ever made a remark about her in front of the SDs the entire decade they were coming EOW, although they claimed to her that I had made fun of her which was a complete lie.  I know this because she phoned my DH and complained. 

Why do they do it?  Hostility, most of the time, and wanting to wrong foot the step parent. Goading them into responding negatively.  

He is allowing this to happen.  He is not parenting his kid. Telling this is disrespectful 

My sd9 does this. Her BM sees her once every couple of years and calls once every couple of months. never talks to her for more than 30 minutes.
anytime there is contact all of a sudden it's "my mommy this" and "my mommy that." 
its frustrating but at the same time I know it's because she is in her own mind trying to cement a relationship with her mother. It comes from feeling insecure because of the LACK of relationship.

this could be what is going on with your SD. She is feeling insecure about where she may stand in the family because there is a new baby on the way so she is focusing on a time (when her parents were still together) because she felt like things were more stable for her. 

Don't take it personally and be patient with her. Gently change the topic. 
 

and told her off she and her sister were completely out of line for non stop ranting on bio mum and stepdad when we don’t talk about them, or ask about them and hubby said they were disrespectful to me as his wife for non stop ranting about bio mum and stepdad when she is irrelevant to us and our household. 

Its like the rants are to make bio mum relevant when she is not. I told hubby i would never go out on meets or family events with his daughters because they constantly tried to undermine me and hubbys marriage and cause issues and hubby originally was too chicken shit to open his mouth 

For the most part I allowed it without comment, but 5.5 years in and a LOT of bad water under the bridge, and now SD13 knows better. She knows to keep the households separated. Typically every winter when it snowed, she would bring up the story of how her father would throw snoballs at her mothers butt. After about 3 years, it got old - same story, plus we had made a trip to the snow ourselves and made new more fun memories...I tease her about how many times Ive heard that story.

Theres a BIG difference between sharing to share, and sharing to get under someones skin.

Heres an example of what should happen:

"daddy tell me about how you and mommy did xyz"

"Hey, how about we discuss something else?"

SS was really bad about it.  He did live with BM for 90 percent of the time so 90 percent of his life was about BM.  We never told him to stop but we did not engage when he wanted to talk about her.  It calmed down some as he got older.  but even  in his mid 20s he talks about her more than I like to hear.  But thankfully he lives far away so I don't have to hear it much anymore.  

I came into my marriage with a child . My daughter rarely brings up her father. So I know children know how to not do that. So when I see children doing it, I know they're just trying to be an ass 

" my mom" says/does XYZ. "my family" (meaning BM, themselves and stepDaddyBigBucks) does this/that

wash, rinse, repeat.

"that's nice."

My 7 y/o SD is the same way but I don't think she understands or realizes that she does it. We usually quietly acknowledge it and move on. It's really hurtful sometimes but I also know it's natural for children to have mixed feelings about having a blended family. I hope that soon she will be mature enough to have a meaningful conversation about it but until then we try our best to be patient or change the subject to sometime related to "our" family.