My sibling has it. It is one of the least treated personality disorders because, by definition, those with it are unable to see a problem.
For me, the best thing I ever did was completely break off the relationship. It was hurting me far more than it hurt her - again, by definition, she could never see a problem in how she behaved or treated me. I was at her beck and call and if I had another committment, like work, I was a "selfish greedy b!1ch".
When my dad turned 70, I suggested we kids give him a big party (he had never had one). She made a nasty comment about having to pay for it - I suggested she could help with the planning. In the end, my aunt and I made all the arrangements and I paid for it all. My other sibling made the cake but of course made sure she misspelled our names and then waited for someone to say something - then she made a huge deal about how busy she was and she couldn't be bothered to spell our names right. On the invitations, I indicated the party was being given by the three of us - even though they had no part in it.
I asked my dad what date he wanted the party and he picked it. I sent out the invitations. My sibling called my dad almost daily for 2 months and complained about what a selfish b!1ch I was for not checking with her first before picking the date. She had to take the night off work and how could I be so selfish. The fact that I had taken a day off work didn't matter. The fact that she was complaining to the birthday boy about how his birthday party was an inconvenience to her never crossed her mind.
The other sibling is manipulative and played everyone in the family. When my dad died, I cut off contact with both of them. My life has truly been better for it. The stress of dealing with them is gone and I am not treated like a servant.
True narcissists are so much more than a selfish conceited person. I still have the dent in the hood of my vehicle where my sibling hit it during a narcissistic rage - had I not locked the car door in time, she would have hit me. Simply because I pointed out that she needed to do an accounting of my dad's estate before she started getting rid of stuff.
RV related - when we met at the funeral home to make arrangements, they started whining about his 5er. He still owed over $30K on it. They sat ther talking and decided that they would just default on the payments and let it get repossessed. When I explained that they couldn't default on it; that all his debts had to be paid off before the rest could be inherited; she gave me an extremely nasty look and asked snarkily "how do you know that?!?". Umm because I'm not an idiot...