Are Lee Marvin and James Coburn brothers?

Despite some physical resemblance and acting role similarities it appears that the answer is no. :)

Marvin was born in New York City in 1924. He was the son of Lamont Waltman Marvin, an advertising executive and the head of the New York and New England Apple Institute, and his wife Courtenay Washington (née Davidge), a fashion writer and beauty consultant. He died in 1987.
https://en.wikipedia.org/wiki/Lee_Marvin

Coburn was born in Laurel, Nebraska in 1928, the son of James Coburn, Jr. and Mylet Johnson. The elder Coburn had a garage business that was completely destroyed by the Great Depression.[8] Coburn himself was raised in Compton, California, where he attended Compton Junior College. He died in 2002.
https://en.wikipedia.org/wiki/James_Coburn