I think screenwriter william goldman (the princess bride) and playwright robert goldman (the lion in winter) were on equal status during their lifetimes, but in different fields.
Anyone else?
A recent conversation has made me want to ask: are there any sibling writers, apart from the Bronte sisters, who are equally eminent? More or less equal, not a pair in which one person is more known as "the sibling".
A. S. Byatt & Margaret Drabble?
William & Henry James?