in the episode where she visits them...

In the pilot, Carol and the girls are living with Carol's parents, whose house is "twenty minutes away" from Mike's. In the episode where they think Jan is allerigic to Tiger, Mike is going to take Tiger to live with "Grandma and Grandpa", and I assume he was referring to Carol's parents. In the episode where Cindy is trying to overcome her lisp, Carol mentions that she had a childhood lisp as well, and it was particularly difficult because she grew up in Swampscott, Massachusetts. In the "Quarterback Sneak" episode, it is established that Carol went to Westdale High with Tank Gates ("Twinkles!"). So maybe Carol's family moved from Massachusetts to California before she started high school. Of course, continuity was never the hallmark of "The Brady Bunch".

I don't remember an episode where Carol visited her parents, although she did visit her Aunt Mary in the show where Alice sprained her ankle on the chinese checkers set.

In the episode where the kids hook up Mike's dad and Carol's mom, Carol's mom is from Kentucky. So, I have no idea how that relates to the preceding reply. Carol may have been born in Kentucky, moved to Massachusetts then before high school moved to California. So, then I guess Carol's mom moved back to Kentucky then visited them. Oh, who knows? You definately can't analyze the consistentcy of The Brady Bunch. Why couldn't Sherwood have been a little more conscience about these things.