reply to Go_Arachnid_Laser
Is “Roy” the name the first character you mentioned was known as? No
Is “Roy” the name of the actor that played the first character you mentioned? No
Is it Roy Rogers? No
Where either of the two sets of characters detectives or investigators of some kind?
No
To summarize where we are right now. We have a TV show with 3 sisters who are not detectives or in a band but who do become entertainers and famous in their fictional world. We have a different long running TV show with Roy, where he is eventually retconned into being the father of the 3 sisters.
Were there any siblings besides the 3 sisters in the first TV show?
Were the sisters orphans or adopted in their show?
3 sisters, adopted, no father… Brady Bunch?
reply to Cheesesteak:
To summarize where we are right now. We have a TV show with 3 sisters who are not detectives or in a band but who do become entertainers and famous in their fictional world. We have a different long running TV show with Roy, where he is eventually retconned into being the father of the 3 sisters.
Were there any siblings besides the 3 sisters in the first TV show? Yes
Were the sisters orphans or adopted in their show? Yes
3 sisters, adopted, no father… Brady Bunch? Yes!
Wait. Is Brady Bunch the actual answer?
Did a show(or some other media) reveal the birth-father of the Brady-girls was a famous character on another show(Roy?)?
If that is the case, I do not know who “Roy” is, but he obviously was on a TV show pre-Brady and it was never referenced.
D’oh, yes, I should have remembered that! The mother’s previous husband was later revealed to have been Roy Hinkley, who was lost at sea and presumed dead.
Not exactly so… 
But if you think of this as a traditional lateral thinking puzzle you can figure it out… even without knowing the reference. Sure you could ask every tv character and figure it out by date, network, random guessing and process of elimination. But that’s not lateral thinking. There is enough evidence from the original and subsequent information here for someone to identify that character right now using lateral thinking, basic TV knowledge, and without asking further questions.
Yes. Sigh. I was hoping someone would think about why they wouldn’t know about what was happening to each other and get it that way.
Did the castaways ever make it back to civilization? If so, there’s a really awkward conversation waiting to happen…
Yes, the Professor is the father of the Brady girls, per A Very Brady Sequel. The Bradys did become famous fictionally when they had their own variety show. The Professor, according to the description from Rescue from Gilligan’s Island was hired by a university when the castaways returned because of his fame and not because of his intellect. So both sets of characters became famous in real life because of their shows, and famous fictionally for bizarre reasons.
And for some reason the Professor did not look up his daughters upon return, nor did his return and subsequent loss again at sea come up with the Brady Bunch reboots. I guess they left their pasts in the past.
Okay, I’ve got one more.
Two cows are standing in a ritzy New York hotel ballroom crowd, mingling while they enjoy their “hay on ice” cocktails. They overhear someone talking about a bird. Why?
Can you explain your previous answer, please. In what way is this “not exactly” a true story? As opposed to not being true at all?
Are we talking about literal cows as in female cattle and a literal bird as in an avian animal? Or like… Scottish human women?
It was true that they became famous in the real world. But they also became famous in the fictitious world.
Actual moo moo bovine cows standing amidst a crowd of partying wealthy New York uppercrust and who overhear something about a bird. No human female references.
Is this in a comic strip?
Print comic?
Cartoon?
New Yorker comic?
Is it a part of a joke?
Was this a real event?
Were the cows part of the reason for the event?
Were the cows there intentionally?
Were they the only non-human animals invited/brought to the event?
Were they there as decoration?
Were they there as part of a tradition?
Was the bird present at the time?
No to all
reply to SurrenderDorothy
Was this a real event? **Yes, though certain, um, liberties have been taken. **
Were the cows part of the reason for the event? Yes
Were the cows there intentionally? Yes
Were they the only non-human animals invited/brought to the event? Not sure, probably no others.
Were they there as decoration? No
Were they there as part of a tradition? No
Was the bird present at the time? I don’t think so…