Yahrzeit for sibling before I was born

Dear Rabbi, Thanks for looking at my question. My parents had a daughter, Leah, who died several years before I was born. I have two older brothers who were alive during Leahs life and old enough to have memories of her. My brothers observe Leahs Yahrtzeit and say Kaddish. Since I was not born when Leah passed, I have never said Kaddish and considered that I have "official" Yahrzeit. (I usually go to shul with my dad and/or brothers and visit my mum) but I dont do the "formal" Yahrzeit actions. I am curious what the halachic perspective on this is? Should I observe a full yahrzeit? Thanks very much for your time.

Shalom U'vracha, The yahrtzeit customs were instituted basically for children to observe the anniversary of the passing of their parents. A brother does not generally observe yahrtzeit practices and customs such as fasting and reciting kaddish. All the best