Well hell...
I was at my step-sister's rehearsal dinner (post-rehearsal) on Friday night a week ago along with about 30-40 other family members and friends who were there. When it came time to introduce me, she said, "This is xxx, my step-sister..." Long pause "This is Stephanie." I pointed at my nose to indicate that she got it, sat down, kept my finger to my nose and bowed my head at the deadnaming. In front of 40 @#$&^%$ people! I was even introduced to someone as "my step-son" by my own step-mother at a different moment in the dinner. I noticed that another step-sister did not use my name at all at anytime during the time I was visiting. And I noticed that the non-naming step-sister's son avoided me, and when we did see each other (I didn't even realize it was her son), and he had that "non-accepting" look on his face. I guess when my step-mother dies (she's almost 82), I will ask the sisters, "So, this is it? This is the end for us?" After 18 @#$%*&^ years...
Whatever... I guess I have to be forceful about introductions, like when I'm meeting someone for the first time in the presence of such relatives, I will pre-empt the introductions myself, like, "Hello, I'm YYY, TTT's step-daughter."
The gift out of all of this is that the step-sister's new husband was graciously accepting of me as far as I could tell.