I'm not sure about Carol's husband,but Mike's wife died.

@manfromatlantis said:

did they ever say were they divorces widowers?

This is from a 'Brady Bunch' website:

Q. What ever happened to Mike and Carol's first spouses, the children's other biological parents?

A. We learn in the first episode that Mike's wife passed away. However, the absence of Carol's first husband remains a mystery. Sherwood Schwartz, the creator of the show, wanted her to be divorced. The network wanted her to be a widow, thought being divorced was too risque for the times. The compromise was that it was never addressed one way or the other.

The Brady bunch movie was suppose to answer it where the caste were gonna wash up on Giligans island and the professor turned out to be her husband.