Have done quarantine twice. But couldn't tell you about doing it with a family. I assume they would put you in a hotel room big enough for everyone. It might be rough with kids however. Back in June 2020, the process took 2 hours. I came back to Korea in early March 2021 and the whole procedure took only 10 minutes. 5am arrival probably helped.
As far as skipping quarantine if vaccinated, right now all I hear are rumors. No need to repeat rumors here. We will have to wait until someone comes to Korea fully vaccinated.