sorry didnt mean to confuse they can live together but they may argue i have almost always had good luck keeping agressive fish together i believe if you start them out young and small and give them enough room almost any fish can get along i said almost any fish some wont get along with anybody
Yes you can. Best to introduce them into the tank at the same time if possible and both should initially be about the same size. The pacu will eventually get larger than the oscar. As said already, they MIGHT rumble with each other so keep an eye on em'.