If I had to guess, I'd guess that you've gotten closer to a point where you don't count the sibs not hating or abandoning their brother as a betrayal of you. This gives them much more space to be close to you.
Also, what I was sort of hinting at before, for some reason, can't quite say why, I'd also guess that they've somehow gotten a more objective/balanced perspective on things themselves -- perhaps because they've had more interactions with XH's GF, perhaps because they have learned more of what went on during the A, perhaps because XH is getting to a more objective place himself and has backed off of demonizing you? (The WASs and LBSs both demonize each other pretty well, lol.) Anyway, who knows.
Here, though, is the challenge you face: as they warm up, you'll feel less needy/less abandoned/less victimized. You'll feel less like the damaged little girl when you are with them and more like a strong adult. The question for the strong adult is: do you really want to have Rs with the sibs? They'll largely be new Rs, and they'll always be some old emotional overhead with them. Perhaps the benefits outweigh the costs for you. That is up to you to decide. They won't ever be just family again though. That can be OK. Just make sure that you feel the choice, own the choice, recognize it as your choice.
Being friends (not family) with Ex-in-laws is not something you "should do" to prove you are healthy. Just like any friendship, such Rs should be freely chosen and welcomed into your life because they enhance your life. If you rekindle (neokindle, lol) the Rs with the sibs, do it only for the sake of that kind of genuine friendship. You don't need to prove anything to anyone here, even yourself. There is nothing to prove.
What about ADD meds? Have you ever tried something like Adderall? I'm telling you, they work quickly (not like anti-depressants) and you can use them only when you want.
As for XH. Again, you have nothing to prove there with respect to friendship. And, trying to be his friend has nothing to do with whether you love him or not.
Suppose a woman is molested by her father. As an adult, she might still love her father, she might even forgive her father, she might be in some amazing place of self-evolution in which she's really dealt with all the old stuff. Yet, suppose she still chose not to have an R with her father. There would be nothing unhealthy about that, nothing stuck about that. There would be nothing in that to suggest she did not love her father or that she did not forgive him. She would simply be choosing not to include an R in her life that wouldn't work well for her.
I think your co-dependence shines brightly when you try to figure out what your Rs with XH and his sibs mean about YOU. Whether or not you should stop being dark, whether you should be friends with EX-family... Your focus is on what it says about you rather than on the value of the R and the other person in the R for him/herself. In a nutshell, you are taking how they react to you, interact with you as proof about something about yourself. It is not proof. They are not you. They are not a mirror for you. You have nothing to prove to them. It will not help you to try to prove something to them to thereby prove something to yourself.
Likewise, if you are never friends with XH, it shows nothing about whether you love or forgive. So, don't worry about trying to prove anything via an R with him.
You are doing great. You are finding some compassion. You are decent and civil to them, kind and loving with Ex-in-laws. You have shed your LoveHimThenYouHurtMe blanket. You are detaching. So don't find another back door to codependence by trying to prove something to you/them by "being friends."
If friendship is in the cards, then CHOOSE it for the sake of the friendship. Full stop. Don't choose it because of what you think such a choice says about you, for that is the back door toward codependence rather than away from it.
Your choices, your risk/benefit calculations, your consequences to own.
