Am due in a few weeks with ds. Bil has a three year old whose name (not actual, for example) is say William Jonathan. They announced him to the world as Johnny, let's say, but for a long time now have referred to him as a different, non name related nickname. We see them probably four times per year at most and the derivative of the middle name is the only name I like for ds and have always done so. AIBU to use it?