Breakdown of Они живут на противоположных берегах, но обеим семьям нужно равновесие.
они
they
семья
family
жить
to live
на
on, at / by (transport) / to (a place) / to (in answer to)
Questions & Answers about Они живут на противоположных берегах, но обеим семьям нужно равновесие.
Why does the word for "both" take the form обеим here?
обеим is the dative case of обе, the feminine word for "both". It is feminine because it modifies семьям (families), from the feminine noun семья. Remember that in oblique (non-nominative) cases, the feminine stem is обе- (like обеим), while the masculine and neuter stem is обо- (like обоим).
Why are обеим семьям in the dative case?
This is because of the word нужно (needed/necessary). In Russian, constructions about needing something put the experiencer (the person or thing that needs it) in the dative case. Literally, the sentence translates to "to both families, balance is necessary."
Why do we use нужно instead of нужен or нужны?
The word нужно agrees in gender and number with the thing that is needed, which acts as the grammatical subject. Here, the needed thing is равновесие (balance). Since равновесие is a neuter noun, we must use the neuter short form нужно.
What case is берегах, and what makes this word slightly tricky?