"I really don't know. I've spent my whole life trying to keep the peace and hoping it will change. I know I'll be forever told as the bad one if I went NC."
And here is your mistake.
You keep on doing the same things, expecting a different outcome - why? That is the definition of madness, you know.
They will never change - they have zero need or incentive to do so.
The only way to change the dynamic at all is for YOU to change - but whatever you do, you're not going to get the "happy family" you so clearly want. It's Not Going To Happen.
So you have to look at what you're getting out of staying in contact with them - you say if you go NC you'll be seen as "the bad one" but if you're NC with them anyway then why would you care? You won't hear it, you won't see it, so why let it bother you?
You're still completely stuck in "appease" mode and as such are making a doormat out of yourself, and now your DD too. You might think "peacemaker" rather than "doormat" but be realistic - you're achieving nothing in the way of peace, no one else gives a shiny shit about your or your DD's feelings, it's All About Your Sister, and she just carries on the same way with no worry about anyone else.
STOP sending presents to anyone other than DN (no need to punish her) - why would you waste your money and time on gifts for people who don't give a shit about you?
I'm sure someone on this or your previous thread has talked about FOG - fear, obligation, guilt - which is what you carry as a result of being brought up by toxic families. Learn what it is and then learn how to dump it.
And STOP playing their game - they're like a bunch of alleycats watching you, the mouse, run this way and that while they continue to swat you with their paws and claws until you die of exhaustion (metaphorically).
Give it up. They'll always be this way and you could do without it in your life.