Learn Russian: Оба брата очень отличаются друг от друга. - Both brothers differ very much from each other.

When using a preposition with the reciprocal pronoun друг друга (each other), Russian strictly places the preposition between the two words. You cannot put the preposition before the phrase like we do in English.

Why does the phrase end with друга instead of just repeating друг?

The first part of друг друга always stays the same, but the second part changes its ending to match the required grammatical case. The preposition от always takes the genitive case, so the second part takes the genitive ending and becomes друга.

Why is the noun брата singular here when the sentence is about both brothers?

The word оба (both) follows the exact same grammar rules as the number two (два). It forces the noun following it to be in the genitive singular, which is why we use брата instead of the nominative plural братья.

Why does the verb отличаются end with the reflexive -ся particle?

The verb отличаться means to differ, describing a state of the subjects themselves. If you drop the -ся ending, the verb becomes отличать, which is an active verb meaning to tell things apart or to distinguish one thing from another.