Taken from Phineas and Ferb Wiki Forum: “Who is Ferb’s Real Mom and Phineas’s Real Dad?”, slightly modified.
I find that Candace and Phineas being half-siblings is actually quite plausible; I refuse to accept, however, that either of them are in anyway blood-related to Ferb, as canon clearly shows them to be step-siblings. My rationale for Candace and Phineas?
- In ‘Little Brothers’, Candace is shown remembering the day Linda came home with Phineas – I believe this is notable in the fact that no other male figure is seen in the picture, as you would normally expect from a Disney family scene. Hence, it can be safely concluded that there is in fact no ‘father’ figure present at this point in time. The name theory (being born out of wedlock, that is) described above would make sense in such a situation; Linda, being a single mother, need not explain the birds and the bees for Candace to understand that she has a brother who is younger than her, and that they’re related. Nowhere is it explicitly stated that they are full blood siblings.
- The relationship between Candace and Lawrence – It is very obvious that she sees him as the only father figure in her life, something that would not be as obvious if she remembered her father in any way; psychologically speaking, Candace was old enough to know the difference between a biological father and a stepfather, seeing as Phineas was at least 2 years old when the Fletchers came into their life, thus their relationship would not be as ‘tight’ as we can see in the show.
As for Phineas and Doofenshmirtz…why not? As I’ve indicated above, Phineas and Candace need not have had the same father at all, so in that context it would not be too absurd for Heinz to have fathered Phineas but not Candace. From my point of view, Phineas and Heinz bear closer resemblances to each other than Candace does to Heinz, so I personally disagree with the ‘divorce and rebound loop’ that some of you mentioned up top.
- Linda and Candace, Heinz and Phineas – The children’s love of music can be attributed expressly to Linda, as evidenced by her ‘Lindana’ persona. However, only Phineas shows any inclination to design and engineering, which in my opinion strengthens the link between Heinz and Phineas, and weakens the one between the bad doctor and Candace.
- “And I never saw her again.” – May not be strictly true; one-night stands may occur entirely without the participants ever finding out who their partner was, particularly when they are inebriated. Heinz has already been proven to drink in “Crack That Whip” (really, the man has eyebags; you can’t expect me to believe his ‘headache’ was from staying up late!) and Lindana being a popstar…in the eighties…yeah, a one-night stand is pretty likely. Also, the 80’s range from 1980-1989, so it is just as plausible for Lindana to have made it big near the 1990 mark, thus aligning Vanessa, Candace and Phineas’ birthdays in logical order.
Speaking of Vanessa:
- Half-brother to Phineas – She was old enough to remember her father working on his Inators (I forget the episode), so that puts her about 5 to 6 years old at the time. My theory on this is that Heinz may have still been with Charlene at this point, and the divorce occurred not long after. Could she have found out about his extremely brief affair? She certainly seems oblivious to his works of evil, so she couldn’t have divorced him forthat.
- On the resemblance between Candace and Vanessa, I think this is purely the artist’s doing – even Stacy has the same basic design, so this is a bit of a stretch, IMHO. For the record, I support Phineas-Heinz due to the characters’ qualities, and not only because of their physical appearance.
Well, all this is off the top of my head and purely my personal thoughts on this topic. I don’t have much to say about Ferb, though, as you may have noticed. Being British and all, we don’t exactly see that many characters with whom we can link the Fletchers. Then again, who knows? Maybe Disney will finally lift the curtain on the past? Well, one can always hope.