Learn Russian: Они скрывают свои чувства друг от друга. - They hide their feelings from each other.

In Russian, when you use a preposition with друг друга (each other), the preposition always goes directly between the two words. So 'from each other' becomes друг от друга, not 'от друг друга'.

Why does the second part of друг от друга end in -a?

The preposition от (from) requires the genitive case. The first друг is frozen and never changes, but the second part changes to match the needed case. The genitive form of друг is друга.

Why is свои used here instead of их for 'their'?

свои is the reflexive possessive pronoun meaning 'one's own'. Because the subject Они (They) are hiding their own feelings, you must use свои. If you used их, it would imply they are hiding some other group's feelings.

What case is чувства in, and why does it end in -а?

It is in the accusative case, plural, because it is the direct object of the verb скрывают (hide). The dictionary form is the neuter noun чувство (feeling). For inanimate neuter nouns, the accusative plural looks exactly the same as the nominative plural, ending in -а.