How many letters does the top answer for “author of all my sons” have?

The most common answer is miller (6 letters).

Crossword clue: author of all my sons

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

miller 6 letters wd-fact-v3

any of various moths that have powdery wings

author of all about my mother 60% similar → almodovar

author of mio, my son 60% similar → lindgren

wrote all my sons 60% similar → miller