Really, it could mean either?
"Their society is very different" means, in English, that their society is very different from other societies.
"Their society is very diverse" means that the members within the society are different from each other and represent a wide range of, or a great many, differences.
Yes. In this series, I had one example where "società" meant "company" and the other (this one) where the official translation is "society".
Fortunately, DL seems to accept either answer as correct, but that doesn't really help my understanding of the language or being able to differentiate between them much...
Yes, "loro" can be both a personal pronoun (used as a subject, meaning "they": they are brothers/loro sono fratelli) and a possessive adjective/pronoun ("their"/"theirs": this is their dog/questo è il loro cane, this dog is theirs/questo cane è loro). When it is used as a possessive adjective, it is invariable and is preceded by the article. Hope it 's clear :)
I was very confused about molto until I decided that if it could mean 'a lot of'the endings would change, if it means 'very' or 'much' they don't. I am sure there are some names for the various parts of speech but it's long time since I studied grammar and I can't remember them.