Learn Swedish: Brukar ni kramas? - Do you plural usually hug?

This is a reciprocal s-verb. The regular verb krama means to hug (like hugging a pillow or one specific person). Adding the -s makes it reciprocal, meaning the action happens to each other. So, kramas means to hug each other.

Is kramas in the present tense or the infinitive here?

It is in the infinitive, because it comes directly after the helper verb brukar. For reciprocal s-verbs ending in -a, the infinitive and the present tense look exactly the same! The regular infinitive is krama, so the reciprocal infinitive becomes kramas.

I see brukar translates to "usually." Is it an adverb?

Unlike "usually" in English, brukar is actually a verb! It literally means to have the habit of doing something. To ask "Do you usually hug?", Swedish asks "Are you in the habit of hugging?" (Brukar ni kramas?).

Could kramas also be a passive verb here, meaning "usually be hugged"?

Grammatically, it could be the passive voice, but in real life, kramas is almost exclusively used as a reciprocal verb meaning "to hug each other." The plural subject ni (you all) also strongly hints that two or more people are doing the hugging together.