arowana hunt above the water.. they eat bugs and things on or above them. they don't naturally look for food below them. they are also independent fish, they don't swim in schools. and the only time they give a damn about another arowana in the wild is when it's time to mate, otherwise all other arowana are chased away.
feed them floating food as much as you can, and either take the second aro back to the LFS or get a FEW more and plan on building an indoor pond in the next year or so.
to keep the one aro from being skittish you can wear dark colored clothing when you are around the tank, you can try to move slowly when you are where your aro can see you. and yes, they can see outside the tank and are aware of their surroundings. keeping the tank dark or dimly lighted for the first few weeks will help, as will floating plants.
if you have carpet in your room you may want to cover the tank so the aro can't see you when you are vacuuming till he gets used to you and they way you move around the room.
and the #1 thing.. KEEP THE TANK COVERED AND SECURE. it's not a maybe, arowana WILL jump out.