Most fans put that theory out to pasture the episode Myra was introduced. It was later REALLY laid to rest the episode that showed how Brock came to be their bodyguard…when he showed up at the compound, O.S.I. was hauling away Myra, and Hank and Dean were already there as infants (IIRC, H.E.L.P.E.R. was holding them.)
So unless Doc Venture somehow had the foresight to save some of Brock’s DNA when they were briefly college roommates, and then cloned that while at the same time cloning his own DNA, which also coincided with ~9 months after he and Myra had sex so she would have some reason to think they are hers, then it doesn’t make any sense that they are clones of Rusty and Brock.
Besides, it’s clear that Hank takes after his mother. They have the same hair, the same nose, and Hank has a touch of the crazy.