Questions & Answers about Каждую ночь бабушка читала сказки, и мы засыпали.
Since the reading caused us to fall asleep, shouldn't these verbs be perfective to show a completed sequence?
For a single, isolated event, yes. You would use perfective verbs to show that one action finished and then the next happened. However, because this exact sequence repeated every night (Каждую ночь), Russian grammar overrides the normal sequence rule. You must use the imperfective verbs читала and засыпали to show the repetition of the entire chain of events.
Is засыпали definitely imperfective? The за- prefix usually makes me think of perfective verbs.
It is imperfective! While the за- prefix often forms a perfective verb to show the start of an action, the verb pair for falling asleep is засыпать (imperfective) and заснуть (perfective). The -ыпа- suffix in засыпали is a classic sign of an imperfective verb, showing the ongoing or repeated process of drifting off to sleep.
Why is Каждую ночь in the accusative case without a preposition?
When expressing frequency with the word каждый (every), you put the phrase directly into the accusative case with no preposition. Because ночь is a third-declension feminine noun ending in a soft sign, its accusative form looks exactly like its nominative form, but we can see the accusative case clearly in the feminine accusative adjective Каждую.
Because both verbs are imperfective, could this sentence also mean she was reading at the exact same time we were falling asleep?