Can I use two past continuous verbs in one sentence?

Yes, for two actions at the same time: I was cooking while he was studying.

Is the past continuous the same as the imperfecto?

Not exactly. The imperfecto also covers habits and long past states, which English often says with the past simple or used to.

Past simple / Past continuous
Past simple	Past continuous
It rained all night. (A finished fact.)	It was raining when I woke up. (In progress.)
When I arrived, they left. (They left after.)	When I arrived, they were leaving. (They were on their way out.)
I walked home and it started to rain. (Two events.)	I was walking home when it started to rain. (Scene, then interruption.)

Past simple and past continuous compared
Point	Past simple	Past continuous
Form	worked, went	was or were plus working
In a story	The main events, one after another	The scene, what was happening
Interruptions	The short action: it started to rain	The long action: I was walking
Signal words	yesterday, ago, then, suddenly	while, at 8 last night, all morning
Two at once	Not used	I was cooking while he was studying.

The Spanish imperfecto is not always the past continuous. Vivía en Salta de chico is I lived in Salta as a child, or I used to live there.
Use the past continuous only for something in progress at a moment. Ask: was it happening at that time?
While usually takes the continuous. When often takes the simple.
State verbs stay simple: I knew the answer, not I was knowing the answer.

Can I use two past continuous verbs in one sentence?: Yes, for two actions at the same time: I was cooking while he was studying.
Is the past continuous the same as the imperfecto?: Not exactly. The imperfecto also covers habits and long past states, which English often says with the past simple or used to.

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