"My brother lives in Moscow."
Translation:Мой брат живёт в Москве.
Russian nouns have different forms called "cases", depending on how they're used in the sentence or what preposition they follow. Москва is the nominative form, which is used for the subject of a sentence. Prepositional case is used after the prepositions в, на, о and при. Москва In prepositional case becomes Москве.
Is it entirely necessary to say the possessive pronoun "my" when talk about ones one brother or sister or parents. Ive been told by multiple native speakers that this is unnecessary and rarely spoken like that. Can we at the very least not mark it wrong when we choose to omit it in those situations?
In Russian there's a rule that works most of the time. Words ending in an consonant are masculine, words ending in an "a" sound are feminine and words ending in an "i" sound are plural. So моя is feminine and мои is plural. It doesn't work like this all the time but it will get you thinking about words the right way.