Worse Than a Crime — Anne Burton

The stain on their name was darkened - with murder... Jock Thorold's daughters openly resented Malcolm, their wealthy father's protege. They strongly suspected Malcolm was their illegitimate half brother - a scandalous matter none of them dared to probe.
That became the delicate task of Richard Trenton, family bank official, when Thorold died suddenly. Was Malcolm legally entitled to a portion of the old man's vast estate?
Richard's inquiry into the private affairs of the deceased led him to make several startling discoveries someone would kill to keep secret.