Gabor Maté does a wonderful job at summing up attachment and authenticity in developmental psychology:
Thanks for sharing the video, very interesting! It seems that when he uses the word "authenticity" he is refering to both internal experience and outer expression of feelings/emotions. Also, I want to mention that when he makes a quick comment that suppressing your authenticity leads to body illness such as cancer, the veracity of that sounds a little questionable.
He ends with asking:
“Who would you rather have in your life? Them or yourself?”
The Epicurean answer: “Myself!”
This sounds like an "either/or" phrasing which can bring up further problems (I see in your post 3 above you explained a bit further regarding that). His phrase makes it sound like one's "self" is in a very delicate and precarious position (a very vunerable understanding of the "self"). Yet as an adult if someone is causing mental or physical harm to me, I must take action to remove myself from the situation or relationship (which could include a parent or sibling).
A possible rephrasing of this phrase: "who would you rather have in your life" changed to "I will make wise decisions for maintaining both my present and long-term well-being". (perhaps lots of ways to say the same thing in a broader way). For anyone dealing with "people pleasing", that likely needs help from a professional therapist.
Also, this metaphor came to mind...that when the airplane cabin loses pressure you need to put on your own oxygen mask first before you help anyone else put on theirs. So it is a matter of placing first priority on taking care of yourself.