Questions & Answers about Брат и сестра отличаются друг от друга.
Why is the preposition от placed in the middle of друг друга?
When the reciprocal pronoun друг друга (each other) is used with a preposition, the preposition always splits the two words. You will never put a preposition before the entire phrase in Russian; the structure is always друг + [preposition] + the declined form of друга.
Why does the second word end in -а (друга)?
In this phrase, the first друг is frozen and never changes. The second word changes its case depending on the preposition or verb. The preposition от (from) requires the Genitive case, so the second part becomes друга.
If the verb отличаются ends in the reflexive particle -ся, doesn't that already imply "each other"?
Sometimes the -ся ending does mean "each other" (like in мы видимся - we see each other). However, here it just makes the transitive verb отличать (to distinguish/tell apart) into the intransitive отличаться (to differ). To specifically state who they differ from, you must add друг от друга.
Could I drop друг от друга and just say Брат и сестра отличаются?