These brothers have no intention of procreating. They have made an agreement to never have any children in order to intentionally kill the Hitler bloodline.
David Gardner, author of the book entitled, The Last of the Hitlers tracked down the surviving Hitler descendants in the late 1990s. Gardner says,
They didn’t sign a pact, but what they did is, they talked amongst themselves, talked about the burden they’ve had in the background of their lives, and decided that none of them would marry, none of them would have children. And that’s… a pact they’ve kept to this day.
Much more at the excellent Today I Found Out, including more on Hitler's heritage and bloodline and related bonus facts and links.