Are we family? My dad's widow and history making me think...(long, sorry)

This one is long - sorry.

I (M52) have a GF (F52) and we have been seeing each other and not quite together apart or whatever that is called for a few years now. Started seeing each other after my divorce about 5 or so years ago. It'll be 6 in May.

I have children, my youngest is 17 and still lives at home. My oldest doesn't live at home and really isn't a part of this except that she seems to have more empathy for him than the one she actually knows. After an appropriate amount of time my youngest met my GF and they do have a relationship. In the beginning it seemed like she was more willing to be a part of my son's life and their relationship was 'good.'

My son doesn't ever go to his mom for help or anything like that, though we share custody 50/50 - if there is a problem he calls me. Even if I'm literally on the other side of the world. He has no faith in his mother.

While I Was away on my last work trip he had a problem he didn't want to stress me with and so he got my girlfriend to help him. That's fine, that's actually great.

My gf was 'fine' with it too. No issue.

Backstory: My Dad married someone I absolutely hated. The why doesn't matter, I tried to have a relationship with her - she was a terrible person and she brought out the worst in my dad. My father has since died and I basically have not continued my relationship with her.

My GF comes from a very close knit family. She doesn't have children of her own but she has a niece and a nephew. She only met my Dad once but she absolutely loved him (and he was really happy to meet her and really liked her too as did his wife) but I was clear, I wasn't interest in having a closer relationship with his wife and though she was making efforts to have a relationship it wasn't something I wanted to happen. I really did not want her in my life. My father passed soon after they met. It was really difficult for my GF to understand my position.

I've been very engaged with her family. Her mom loves me. Because of the distance between our two homes though and the fact that her brother and his children now live with them too - I don't spend the time I used to at her place. We spend our time together mostly at my place. It's not terribly far but the traffic is brutal and it can easily take over an hour to get between homes. In the beginning I used to spend the night at her place but over the years things have changed and that's just not really the option it was in the beginning.

Now to the problem.

I made a joke about us being a family because from my perspective, we are. She has a long term relationship with my son that matters to me. My relationships with her family matter to me. It matters to me that her mom cares about me so much. It's part of what makes her her and one of the reasons I love her. So I referred to us as a family and she got quiet and while she did not say she didn't agree, I can see now that she doesn't agree. She may consider me part of her family - she doesn't consider my son part of her family. I've also been pushing my son to not do his things in the house as much when she is around (he's a musician, we built a studio in one of the rooms and it can get pretty loud because sound proofing is expensive). I have noticed that this is impacting his home life and I've noticed that she complains about him and when he has friends over more than I'm comfortable with.

The realization made me think about how much I genuinely dislike my dad's wife and how much she impacted my relationship with my dad. I am extremely close with my son. I don't want that to change. She doesn't think of him as family though and I know he thinks of her as a trusted adult, perhaps even more so than his own mother.

We actually have a trip together with the three of us in about a week over the weekend. I'm on edge about this.

If she isn't going to consider my family part of her family - at least my youngest son...

ugh.