Is it usual to have an aliyah and make kiddish for a Parent’s Yahrzeit on the Shabbat BEFORE or the Shabbat AFTER the Yahrzeit. Thank you

Shalom, Thank you for your question. The custom is to receive an aliyah to the Torah on the Shabbat before the yahrzeit. As to the kiddush, if local practice is to provide a kiddush in memory of the departed on Shabat, then it too will be on the Shabat before the yahrzeit. Some communities have a custom of providing a small “l'chaim” on the day of yahrzeit after Shacarit. But you should follow local custom in this question. Blessings.