Questions - Spoilers

This was a good movie, but I couldn't quite figure out a few things. Maybe I missed something in the subtitles or overlooked something trying to read them...

Was Dae-yeong's mother is prison for 3 years, 7, or 20? I thought I saw references to different numbers. 20 years sounds way too long for pick-pocketing.

Did Dae-yeong's and Jang-mi's mothers know each other? Were they sisters? (making Dae-yeong and Jang-mi cousins)

What was the relationship between Lieutenant Oh and Dae-yeong?

Why was Lieutenant Oh friendly towards Dae-yeong's mother when she opened up her restaurant?

Are Korean police actually allowed to openly beat suspects?

It seems like Dae-yeong could have called the coast guard to stop Jang-mi instead of shooting at her boat.

Please let me know if you know any answers or have any theories. Thanks!