How do I begin to heal from the past so that I can build up my self worth and confidence?

Recovering from invalidation and living with people of whom have narcissistic traits can be challenging to navigate. To your points, living with someone with these traits makes us feel as if we have to be cognizant of every move, action, and statement that we say. This can also create confusion in recognizing our own needs, as anytime one attempts to speak their truth, their sanity is questioned. You have mentioned some examples of this, such as, "they don't realize that they're doing it." When the blame is placed on someone of whom is attempting to respond with healthy limits, it creates the false belief that setting boundaries is a bad thing. This results in one of two responses: either folding, obliging, and becoming externally obedient to keep the peace, or, rebelling and losing some of the relationships in life due to anger and frustration taking hold. There are effective ways that such instances can be approached by applying healthy personal boundaries.

Personal boundaries are the limits and rules that we set within relationships for ourselves. They allow us to recognize what we're okay with, as well as what we're not okay with in personal relationships. Personal boundaries also allow us to determine ways to communicate our needs and wants through words first, and then actions second. If we're too porous with our boundaries, we fall into the trap of being compliant (thinking that "no" is a bad word because it causes others to be upset, therefore, politely denying ones needs to keep the peace"). If we're too rigid with our boundaries, we fall into the trap of what's called stonewalling (thinking that people and the world should always conform to our needs because of the anger that we feel, therefore, telling people that there is only one way). We can find a nice blend through use of healthy boundaries (prioritizing your needs, wants, and feelings, while also listening to and respecting the needs, wants, and feelings of others, without behaving passively or aggressively). 

In essence, healing from the past is leaning into what you will vs will not tolerate from your sibling and family, and empathizing with the distress they may have, while making it clear that it is their distress. This may look something like the following: (speaking to your father) "I see it upsets you that I choose to create this space, however, I will not tolerate being treated this way anymore by my sibling. I choose not to apologize to them because I am not in the wrong." The harsh reality is, the boundary will teach you the quality of the relationship with your family, and in turn, what it is you feel would be best for you to take in and receive the good that exists out there. It's asking ourselves whose love do we potentially have to miss out on if we choose to live. 

I'm so glad you're doing the work of boundaries, and cutting the cord due to recognizing they may never change. Boundaries have nothing to do with us changing others. They have to do with changing ourselves so that we're no longer affected by those of whom treat us poorly.