Just my opinion or guess it is their comfort zone to think of you as a "family" as you are now. I do have one questions will the new baby use the same call name for your parents? We adopted older children and hindsight is wonderful, I think if I had them use Grandpa/grandma, Aunt/Uncle would have made them feel more in the loop.

Doodle, my guess is it's probably a little bit of both: the girls still not fully grasping the concept and perhaps a bit of some natural insecurity about their circumstances being 'different' and/or worrying their 'cuteness' may be temporarily displaced. If it was me, I would just keep on correcting them as you have been doing, because it's not going to be practical or desirable to go along with the untruth that they were actually in your belly. It's important that they come to accept and understand that just because they weren't in your belly doesn't mean they are less important to you and their dad than the baby. And at the same time, I'd make sure and throw in something like "no, girls, I didn't get to actually have that experience of seeing you when you were first born, but everyone tells me how totally adorable you both were, and I sometimes like to picture it in my head." That would reinforce the actual facts but in a way that gives them that extra bit of attention and praise that they will probably need for a while with a new baby on the way.

I don't know that it's something to worry about. The girls start asking me if I remember when they were babies, when they were in their mama's tummy, . It sounds like they've got the basics down, they know they were in their mama's tummy not yours. They don't remember their life before you were in it, and I think 5 is maybe a little young for kids to really be able to understand "time before I can remember" and that things used to be different. Heck, about a year ago, I was talking to my SM about my little nephew not really talking yet, and mentioned well remember my brother (his dad) having been just like that at that age completely forgetting until she reminded me that she wasn't around when DB was that age. And I'm a grown adult, and I actually remember the time I was talking about.

I think it is going fine, and I love the names -- they show genuine affection.

This is a very interesting topic, and one that has been coming up in our house, too. DD5 doesn't seem to "get it" that I'm not sissy's (SD15) and SS18's mom. Even though sissy just started living with us this school year, and even though she knows that they go on the airplane for visits. And they both call me by my first name, not Mom or any version thereof. Just the other day I asked SD15 if she told her mom about something at school, and DD pipes up from the back seat, "you're her Mom". I think it's just a developmental milestone that is a little further down the road. The idea of her sibs having 2 houses, 2 moms, etc, is clearly unimaginable.

I think their questions are perfectly normal..they are probably still putting together in their heads what a "family" is. I can totally relate to your situation having raised SD fulltime since a toddler and also eventually having biological children with DH..this is how I handled it and I think it has turned out well (she is now 11)
first, I explained to her that families can come to be in many ways, some children live with both their biological parents and some dont and one is not less than the other, blood doesnt make you a family it is the time spent together, the loving and the taking care of one another that makes you a family.
As far as questions go about when she was little and I wasnt around (and I got many, thats why I think your girls are right on target) it really depended on the question..if she asked was she a cute baby I repied "of course you were a beautiful baby, here lets go look at a picture of when you were a baby.." I also made an effort to learn as many stories about her when she was an infant, and about her birth for times when things like that came up..when she asked what time she was born I told her the time..when she asked if she cried a lot as a baby I started off with let me tell you a funny story grandma told me about when you were a baby and you cried.... I gues what I am trying to say is that I have always tried to answer all her questions that I can while still making sure that she knew she had a BM.....there was one I couldnt answer when my DD was born...she wanted to know if she was nursed like her little sister..I told her no and she asked why?.... i had no idea so i told her she would need to ask BM that question next time she saw her....there are some things you cant answer and thats ok too....
This will be a tough transition for them with a new baby coming...one thing that I told SD when our biological child was born and she was upset that she wasnt my biological child was that she was sooo very special because I didnt get to choose my biological children but I did get to choose to be her SM...and I chose to be her SM because I loved her so much....that was back when she was 6 and even to this day she will still pop up and declare proudly that her mama(she calls me mama and BM mom whole nother story..) got to choose her.....I think it made her feel special when she was feeling a bit left out..and i think it still makes her feel special......
another thing we did was stuck to the names everyone in our extended family already had whe nwe had biological children....I think it was awise choice because all three of kiddos call nana the same thing and no one is "different"

Thanks ladies:) I pretty much assumed what you have said. I just keep correcting them and saying things like "No but we have seen pictures and you were too too cute." We did actually pull out a couple of their sonogram pictures last night and looked at them all crammed up on the couch. I said "Well now I HAVE seen you in mama's tummy." and they seemed happy about that. We busted out their baby pictures as well.

I think they really don't remember too much about the B.D. (before doodle) days and they are trying to grasp the concept that families change sometimes. Jonathan didn't know how much in detail he should go with the explaination so we just told them this. Families can change. You never LOSE family members but you can PICK UP new ones along the way. That's why families are unique. You can only EXPAND them.

I have all kinds of anxiety about how a new baby in the mix is going to go over with everyone so I am looking for any clues of insecurity. I do not want the girls to feel like they have been in any way pushed to the side by Jonathan and I or my family. Those little feelings are tender.

KKNY- Pirate and Gangam are hillarious names and they totally suit my parents. When J picked the girls up from school the first words out of their teachers mouth was "Who is Pirate and Gangam?" HAHAHAHAHA. It all made since to her when he said "That's my wifes parents." They must of been talking about them all day at school. They really have clinged to my family.

All the grandkids call my mom and dad Gangam and Pirate. If you could see my dad you'd get the pirate thing immediatly:) He LOOKS Like a pirate.

P.S. Nadine decided she wanted to be a pirate for Halloween last year and is trying to talk us into letting her be one again this year. She hero worships my father:)