When I mouse over the word "Frau" wife was one of the translations. Then why did I get a wrong answer?
Do not trust those translations that much. In several cases they are wrong but most of the time they are out of context and cannot be used.
Frau can be Woman or wife. But it's pretty much always woman if it's just an article in front and wife if it's a possessive. But yes The hover translations are just a guideline you can't solely go off of them
why can Frau not be wife here? Must Frau (woman) be 'possessed' (in the possessive) in order to be a wife..?
Duolingo probably expects either husband and wife or man and woman
Strictly speaking, you have a lot of 'stuff (eg sugar)' but you have many children; If it's countable then it's many / If it's measurable (by weight or volume) it's much or a lot.