I think that Franco isn't Jason twin brother I think his Heather son. This is my theory Heather left Port Charles in 1983 the same year that Susan Moore was killed. That same year Heather was sleeping around with Scott Baldwin. Heather left town and found out she having another baby and she was having it with Scott but Scott and Heather ain't together anymore so she gave birth to their son. Karen Anderson Franco mom was in the room who was probably a nurse so maybe Heather gave Karen her son and Karen named him Robert Frank. Karen might of let Heather see her son. Then one day Franco saw video of Jason so either Heather or Karen lied and said that was his twin brother. So Franco became obessed with Jason. I think Heather wanted to keep quiet about the Franco I don't think Franco knows that Heather is his mother. I think Heather lied to Sam about Franco being Jason twin. But I think that Jason does have twin brother. His my theory on that If they do recast Jason that will probably Jason first then if Steve Burton wants to come back then he will be the real jason and the fake Jason will turn out to be his real twin brother. I think Heather is wanting to tell Franco that why she wants to see him.
Ok i'm watching today's GH and Heather tells Scott that Franco is his son. I was wondering how, because I honestly can't remember them being together (although I've been watching GH for 32 years). So what you said here makes perfect sense. So now they get to write in a new twin. Perfect ending to the 50th anniversary year.