Why are phenease and ferb stepbrothers?

well no one really knows. but i think it's because Phineas' mom got divorced and so did ferb's dad then they got married.

ferb's dad and phineas' mom got married probably afta a divorce

I think it's because they born in a different parents but after phineas's mom n ferb's dad are single then they got married

Maybe cause the producer wanted them to look different but same age, so they made them as stepbrothers....