Andre and Ben have been dueling since they were small children. Their older brother is a pro on and off with his tag partner. Andre's backstory that has yet to be revealed had him dueling A LOT due to his uncle. Dueling, especially tag dueling, was a big part of their family history. If they learned nothing at all from tag dueling on the streets when they could and watching their big brother play in the big leagues then they're pretty piss level duelists. Ben himself is the least skilled out of the bunch of them and half of it is because he likes people to have a chance to duel bringing out his big guys only when he needs too. All of the Carson siblings have a big backround when it comes to dueling and Andre has the advantage of having played with different decks or having observed them being played. The one thing is Ben who has done nothing but warriors half the time. He finds the basic stuff boring because he's seen it done but he still hopes there are ways he didn't know of like the various elemental heroes and he's never seen a contact fusion before. 

Andre knows the synchron combo because he had it used on him in the past and he got his ass whooped because of it during one of the pre-stated backstories. He refuses to use it because he's edgey like that and doesn't like following the same rhythm as everyone else why else would he have ARCHFIENDS as his archetype. Likewise even if he wasn't like that he'd be stuck with a basic synchron deck off the bat and he doesn't like using decks half cocked. Archfiends in his opinion are meant for all out brawling and even at their current stage. Why they're here is because Andre wants come credentials on his resume and Ben's here to make sure his brother goes through it alright and he himself is curious too see what he can learn. 

As for Andre's attitude...he's an asshole who thinks if it isn't obvious enough to everyone at hand that they really are beneath his time. It's not a matter of him knowing it or not it's him viewing others as beneath him. Ben finds fusion boring because big shock there are no warrior fusions he's really interested in seeing come out outside of the buster blader archetype. When was the last time anyone actually used flameswordsman? He prefers easy Xyz summons or ways to find out how to bring out Xyz monsters as he likes the concept of taking his smaller guys and making bigger guys out of them. Andre sees his units as chess pieces, archfiend chesspieces not withstanding, and if he needs to sack a couple of his guys to get the 'king' piece or the player in this case then he's perfectly willing to throw his archfiends into the banished zone so his Emperor can go on a rampage.