Concerning the amount of flour required for hafrashas challah, we recently read that when using whole wheat flour, one should add a certain amount because during processing the bran is removed from the flour and then put back in. Is this true

One would need to check with each flour mill. From what we currently know (and this may change, so check from time to time), at the Rubinfeld and Mehudar mills they don’t separate the bran from the flour and so there’s no need to add to the amount. Regarding other mills, one would need to verify directly with them. Generally they separate between 12-18%, and so one would have to add that percentage to the flour.