I umm stumbled upon some theories for a TV show called phineas and ferb, and well... (notes and credits!!!)
Ok um first ill have to explain the show: Linda, Phineas and Candace's birth mother is remarried to Lawrence, Ferb's birth dad. So basically, Ferb isn't related to Phineas and Candace, and neither is vice versa. Dr. Doofenshmirtz is an evil scientist who is currently divorced, with a daughter named Vanessa. He used to be married to Charlene. So anyway, I saw theories on who Candace and Phineas' birth dad, and welll................... Oh what in the- Ok, ok, I guarantee you this isn't valid, but here we go... The theory is that Linda (P and C's mom) was married to Candace's dad, right? Well, at one point, Linda and Dr. Doof had a date (AGAIN, DOOF SAYS THAT THEY NEVER DATED AGAIN, SO THIS LIKELY ISN'T TRUE!!) And ANYWAY,,,, the theory is that Linda divorced Candace's dad... Due to non-kid friendly reasons... And Dr Doof is Phineas' dad. It makes sense though, (look at the project!!) Because Phineas builds stuff like Dr Doof does, he must've inherited that! And they do have similar head shapes. And hairstyles, that look like palm trees. They both have dark blue eyes (although nearly every character in the show does) same skin tone,,,, etc..... SEEE? SEEEEEEEE?????? WHYYYYYYYYYYYYYYYYYYYYYYYY