Q. If there is a number of sons and daughters of a deceased father living together, does each one have to light a separate candle on the day of the Yohrzait, or is it enough with one?
A. Kol Bo (p. 398), quoting Moed Lechol Chai (p. 34), mentions that in principle one light for all children would be sufficient. However he adds that when possible it is preferable that each child should light their own light to honor their father.
Horav Shlomo Miller’s Shlit’a opinion is similar
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a