Just to clear things up, Frank and Ken are stepbrothers. Ken was put in to multiple foster homes until he found bob Shamrock's foster home. When Ken was 18, bob adopted ken. Frank is younger and they found him later. When Frank was 21, Bob adopted him.
Anyways, now it would definitely be Frank, by decision. Ken would not be submitted, or knocked out.
In their prime, it would be a war and I can not decide who would win in my mind.