So the Alaska is a e175 which is about 70 people vs the United which is about 170 people. It looks close because of the angle and some camera tricks. Landing on parallel runways happens all the time.
They are called Precission radar monitoring approaches and they start doing them when things get super congested. Requires us to listen to another radio so atc can tell us to break-out if someone crosses the no go zone in between the runways.
Two airplanes landing at the same time with close proximity (i.imgur.com)