Welcome to SR!
I am a hard-wired codependent and I struggle daily with codependency even though I have been in recovery for years and years.
So I just want to remind you that you always have the right to CHANGE YOUR MIND. If you take on a responsibility that does not belong to you, and you realize you've made a mistake doing so, you can HAND IT BACK.
You may not always make the automatic right and healthy decision. But if you make a wrong decision, you are never trapped there. Just shift gears and turn that buggy around in the right direction. Don't worry if people are upset with you changing your mind. As long as you know that you are doing the healthy action, and are being authentic (as opposed to being fake to please people), you will be able to do whatever you need to do to maintain your recovery.
All that brother/long lost sister drama: I can't see how it adds anything positive to your life.