From what you wrote here, I think your mother was also direcly emotionally abusive, by blaming you for her own choices and actions. I feel angry with mothers like this, like mine, who put their children through all this lying and blame. You and your siblings were not treated as you should have been by either parent, whose most basic responsibility is your emotional and physical safety, especially in the home.
Your birth timing had nothing to do with who she chose to marry and have kids with. A series of choices and lies were made prior to your birth. I'm sorry! But none of this was your fault, and your name on the forum ought to be immediately changed. You don't deserve it.
Nor did the fact that you arrived later than everyone else and got spared some of the intensity of abuse from your father mean you didn't also get negatively affected by the family dysfunctions and dynamic.
The very fact that you are expressing "Survival Guilt" which your whole post is about, is ample evidence of having survived a traumatic family environment. It matters very little if you recall physical of merely emotional violence. It's going to take work from you to process and heal. Emotional scars hurt so much more than physical ones.
It's time to see that none of them are or have been able to be honest with you about who they are, as addicts. It's going to take some therapy and time to weigh how growing up in a traumatic environment has impacted your thinking now.
I think a lot of us can relate to your survivor guilt. :( This is a phase of the healing that is normal with PTSD. You are okay for having these feelings. Just remember that. All the healing you go through, has to be gone through, as a thought process, in which you begin to see your reactions and emotions for what they are--healing. Don't judge and push away your emotions. You did right to post them here where you can be validated, maybe for the first time, as you should have been all along. :hug:
I think survivor guilt is a form of the grief stage of denial. With addicted parents who live in a bubble of denial, manipulation, and guilt, denial is a huge problem for those of us raised this way.
Denial is a protective response; don't rag on yourself for it; just learn to feel when it's happening and work around it. Don't make excuses for others. Rather than getting down to the pain you are really in, you focus on the others (as a kind of distraction). It feels like you can't heal yourself because you have been brainwashed and guilt-ed into worrying about the rest of the suffering family members. It doesn't even matter if they are the cause of that self-inflicted wound! See it for what it is, and realize you can't help them. You can only help you, and that's what you can choose to do now. You can put boundaries down and walk away from those who are keeping you stuck in the past.
I find this to be a very common reaction to trauma in those who grew up with it and who wish to find ways of relating to dysfunctional people, which was the only way to have relationships growing up. This is not "codependent" so much as what you gotta do to maintain relations with less than healthy supporters in life. Point is, now as an adult, you are not stuck with that family unless you want to be. Nor are you stuck with the identity they gave you. You can't change the color of your skin, your family background, disabilities, or illnesses, but you can change almost everything else about you. That's powerful!
Have you read about or experienced recovery or addiction from the adult child of alcoholics? While I disagree with some of 12 step and "adult child" definitions, it does help survivors gain a reframing tool to see the traumatic family dynamic for what it was and to step away into healing place.
So I think grieving the childhood that we (I didn't get it either) needed, did not receive, and will never have is a major step in realization of the traumatic loss and grief process that is needed to grow, heal, and realize potential. Denial is one step that gets processed, and you are processing it.
If you are not in therapy with a trauma therapist who has training in complex trauma and who you feel safe with, you will need some support to go through this and come out better off. An AA local group will have resources in USA for those of us hurt by addictions in caregivers. I'm not sure where you are at. Also, this forum is also a great support if you use it as such. I know you will find help here.
Welcome, Muse