I'm not referring to the "old" Mike/Carol (https://www.youtube.com/watch?v=XvzHHdOc1IM) couple (https://bradybunchreviewed.wordpress.com/2018/05/25/episode-21-youre-never-too-old/). I'm talking about Mike's dead wife's family or Carol's ex-husband's family?

After the first season its almost forgotten its a blended family. The only time you hear the word "step" is in one episode. The kids never refer to their siblings as step sister or step brother. Other moments during the show its inferred they are all biological. When Greg is upstairs practicing his guitar, Mike comes home and greets Carols at the bottom of the steps. Carol says something like talent runs in her family. In another episode Jan tells Peter that blood is thicker than water in trying to get Peter to help her. They are not biologically related. Bringing outside family into the show would highlight the blended family again. Season 1 was all boys vs girls and the struggles of a blended family. Season 2 it was no longer boys vs girls and we got to see each of their own problems. By the time season 3, 4, and 5 came around the show had turned into something completely different.

Ya its kinda nice how they all accepted each other as thier own :)

After the first season its almost forgotten its a blended family. The only time you hear the word "step" is in one episode. The kids never refer to their siblings as step sister or step brother. Other moments during the show its inferred they are all biological. When Greg is upstairs practicing his guitar, Mike comes home and greets Carols at the bottom of the steps. Carol says something like talent runs in her family. In another episode Jan tells Peter that blood is thicker than water in trying to get Peter to help her. They are not biologically related. Bringing outside family into the show would highlight the blended family again. Season 1 was all boys vs girls and the struggles of a blended family. Season 2 it was no longer boys vs girls and we got to see each of their own problems. By the time season 3, 4, and 5 came around the show had turned into something completely different.

As far as Jan's comment "Blood is thicker than water", it's not too out of line, often times a non-biological family will start THINKING of each other as blood family after a while. I'd say there came a point where they wouldn't think of themselves as "technically not biologically related"

As far as Jan's comment "Blood is thicker than water", it's not too out of line, often times a non-biological family will start THINKING of each other as blood family after a while. I'd say there came a point where they wouldn't think of themselves as "technically not biologically related"
I sort of disagree. Blended families always know they are not related. It was the writers of this show that post season 1 made us all feel and pretend they were all related. Every person I knew that had a step mother or step father referred to them by name not mom or dad.
I believe it was Chris or Eve that actually protested with writers about that line "we are not related" and their response was .....everyone forgets that now.

But isnt it nice all they all treated each other like they were always the same family?

But isnt it nice all they all treated each other like they were always the same family?
Yes. Both Barry and Chris talk about this all the time on the podcast. They wanted to get mad at their sisters like real step brothers would and say "you're not my sister."
After season 1 (boys vs girls), the viewer is led to believe they are a related family, Except for the lyrics to the theme song, a new viewer would never know they were a blended family (outside of season 1).

We should nominate most likely to have played the grandparents!!! Older, big stars of the time.