My dictionary tells me that "member" is "Mitglied" and "members" is "Mitglieder". Duolingo says that "members" is "Mitgliedern". Which one is correct?
So is it safe to say you are supposed to ad an "-n" for all plural dative nouns?
Only if they don't already end in an 'n' in the plural, or if they end in an 's' (den Autos is fine). Also, some take '-en'.
Why do we use "Mitgliedern" here instead of "Mitglieder?" Is it because "mit" turns this into the dative case?
I'm a little confused as to when to use "den" and when to use "denen" in plural? Can someone give me an example and a brief explanation of each of the two, please?
"den" is the dative form of the plural definite article "die" (=the), "denen" is the dative form of the plural pronoun "die" (=who, which, that).
er trinkt mit den Mitgliedern = he is drinking with the members.
da sind die Mitgliedern, mit denen er trinkt = there are the members with whom he is drinking.