The first video is of HEMA (Historical European Martial Arts.) HEMA members study texts written by people who studied and taught swordplay and other weaponry back in the day. Type HEMA into Youtube and you'll find all sorts of awesome examples!
As for OP's question, the HEMA group I attend focuses on German longsword, which is basically what the people in the GOT video are using. I've been practicing for a year. I'm no expert, but from a brief look at the video there's a few things that stand out.
First, as a few people have pointed out, the actors are telegraphing their moves WAY too much. This is so you, as the audience, can SEE what they're doing. Which is exactly what you DON'T want when you're in a fight. If you're opponent sees you pulling back to build up momentum for a great big swing then they have plenty of time to react to it. It's really amazing how fast your mind can process even slight movements. The shifting of your foot, a leaning to the side, the subtle flick of your eyes. The tiniest movement can give away your play and suddenly they've a sword in your face.
I've watched a few sporting bouts at my school. The instructors will record the bout from multiple angles and watch it later because the naked eye cannot parse the blows in real time. This, of course, would make terrible TV which is why the GOT actors make such big movements.
The second thing I noticed is the duel wielder. Now, let me start by saying duel wielding DOES exist. Some people like to claim otherwise. But you can find it in a variety of Asian martial arts, krabi krabong and Eskrima for example, plus rapier and dagger if we want a European example. That said, a longsword is NOT cut out for duel wielding. You're gonna have a hell of a time trying to block a blow one handed with a longsword.
Finally, if I were up against duel-wield-guy, I'd just flank him. There's what? Four against one? Even with two swords he's two swords short. Guy's dead. You're not leaving that unscathed. Especially if he keeps spinning his swords around. That's an attack of opportunity if ever I've seen one (or a "nach rising" opportunity, if you want the proper fencing term). Oh, and he spent like 5 seconds stabbing the third guy through the chest. 4th guy has plenty of time to lob his head off while he's busy.
Oh! And one last thing. Getting stabbed in the gut is probably fatal, but not necessarily immediately. It can take days to die of a stab wound. If you stab your opponent you better follow up with something else because they can keep fighting until they bleed out or die of septic.