User blog comment:Kuzlalala/Lala's Long but Orderly Put Theory about Phineas and Candace's Biological Father/@comment-80.222.101.236-20110812103535/@comment-184.5.201.81-20110818030514

No... because Dan and Swampy said they were step-brothers. They didn't want twins, or anything like that. So they decided to make Phineas and Ferb step-brothers.