Losing my friend to her sister?

As a heads up, I'm not the best at grammar and I have trouble stringing thoughts together. I was always told 'don't trust your brain after 9:00pm' so I'm bringing my troubles to reddit.

This is a strange place I find myself in. I (27 f) have been online/irl friends with a person (26 f) we will call Abigail for this post. She and I met online through an online art collection website when we were children with way too much unrestricted internet access. We have been friends since 2012 and I can confirm she is who she says she is lol. We have met up numerous times in person with other friends throughout the years, riding out covid and adulthood together. I come from a disjointed family with multiple households and several siblings. She comes from a (mostly) stable home with one sister (19 f) we will call Flora for this post.

Within the last few years, Flora has been joining Abigail on her visits to our once to twice a year meet ups. Abigail and Flora live several states away. It was fine at first- and truly I believe is still fine as I like Flora and at some points feel like she is a distant sister to myself.

Abigail and Flora have had a good relationship growing up, but ever since Flora started college it seems their sibling relationship has blossomed to a point where they almost are glued to the hip, even with Abigail living away from their parents house, and Flora living with their parents or a dorm.

Abigail and I used to talk everyday, play games or watch movies twice a week, or even just audio chat through discord. We would also rp our fanfiction and dnd campaign characters almost everyday since 2014/15. Basically running little micro campaigns/stories between us- almost like a modern version of playing with dolls and action figures haha. We would even draw art of our characters and share songs/media that reminded us of them.

Just within this last year I've really noticed everything fading. It's so hard to find time to connect one on one without Flora being invited or automatically added in. I didn't mind it at first- I actually liked it a lot and connected well. I'm glad they have a healthy loving relationship. I'm very disjointed from my siblings (all 9 of them) but I don't hate any and none hate me as far as I am aware, we just don't hang out often as we are all building our own lives.

Recently I noticed the few audio calls we are getting together is mostly Abigail and Flora talking about their own lives- people I don't know, events, concerts they went to, artist they like, things that happened that I have no concept of (from being states away) local places, food, activities. I do try to chime in but there's only so much I can say. I have even once or twice said something akin to 'sorry I don't know how to contribute'. We did have a through line for a while- all of us work in a very niche industry/company just different fractions of it. So we could talk about our different experiences though with Flora and Abigail being from the same unit, it makes more and more conversations mashed into 'did you see x do y today?' and when I try to mention events, I get a 'ours doesn't do that/that's crazy' and not much follow up. I've stopped bringing it as a conversation point into topics unless asked.

This next part is silly and has to do with Dungeon and Dragon Character roleplays, so you can skip it if not interested;

They're also rping their campaign characters (we are all in the same one) now and while I don't mind as I also rp my campaign character with other members from time to time (including Flora) it is affecting conversations a bit. I.e. We were watching a show in audio over Discord and I mentioned the two main characters reminded me of Abigail and I's dnd characters- to which Flora made a sighing noise and mentioned hers with Abigail's. I took it a little bit like it was passive aggressive tone? its not the first time, but I am suspecting their characters are dating within the campaign or Flora implies she would have liked their characters to be a cannon couple. Problem is Abigail and I's campaign characters are in an established couple in the game- and I don't really want to feel like it's that serious because it isn't, but it gives me a weird vibe that they are rping a couple behind my back. To preference; I don't think nor will entertain the thought of that being anything more than having fun with characters, nothing sexual/incestuous. Just kind of feels like a fake-cheating kinda feeling. Again not that serious but still is stacking onto the things I have been feeling.

Back to more real life things;

She did reach out yesterday to check on me when I mentioned in a group discord about how rough I was having it that day with my brother going to prison, work stress, and generally trying not to cry in a public space. She and I had a good private DM talk where I felt much better and it felt good to talk with her one on one again. She said if I needed any distractions this week, to please reach out to her.

And I did, day after (today) as I had a terrible night with my puppy needing to go to the emergency vet- he's fine now, but he injured himself and sustained a tooth fracture and laceration, but it was scary and I was covered in saliva and blood for a bit. I also went to my family to deal with the next steps regarding my brother's future as a felon, and had to attend a work teams meeting to deal with a difficult project. All in all, a stressful night leading into a stressful day. I asked if we could play minecraft but she's busy with her sister on an art project. That was just... kinda rough. Especially since she offered less than 24 hours before to help be a distraction through this difficult time. I didn't push the conversation, and they offered an hour later to audio call through discord for the three of us. But I really just don't want to loop Flora into my personal drama- as what my brother did was very bad, and I still view 19 as a minor and didn't want to discuss those things around her- again both Abigail and I being in late 20's, didn't feel appropriate even though Flora is a legal adult. Though I am sure Abigail already told her a version of it.

I'm also certain if I hoped into that audio call, I would have sat there while they chatted about whatever again. It would have been easier if we had all been playing minecraft or watching a tv show, as there would be some neutral subject for us to connect on.

So my question is; how do I handle this? I am not unrealistic and I do understand that Flora is Abigail's one and only sister, and I am a friend. Her bond is stronger and deeper with Flora, and I shouldn't approach this situation with anger, that will only make it worse. I'm just not sure how to rebuild the level of friendship I once had with Abigail without upsetting Flora- because I do like her! Like I said, she feels almost like a long-distance sister to me. I'd also like to hear from anyone who had a similar situation and how you progressed through it. If your relationship is still strong, faded, or what have you.

(And if there is any dnd/rp'ers out there, your advice on that one specific situation with them is appreciated)

edit; Someone mentioned to put this in here instead of the previous area. Thank you!