I wil try to correct some of the mistakes, because I am not a teacher.
First of all, your question should be "Are these sentences correct?" You don't need to repeat the word "Are".
- "Affluent" is an adjective, therefore, you cannot pluralize it by adding the letter s. However, according to Oxford Dictionary, it can be used as a plural noun without s. For example, "only the affluent could afford to travel abroad." Please note that the same thing goes for the word "poor".
- After the adjective "advanced", you need to put a noun.
So, in my opinion, the first sentence should be like this "The affluent in advanced countries were suffering from obesity. In contrast, the poor in underdeveloped countries suffered from hunger."
My reply is getting too long. I'll continue in another reply later.