There is no secret, no tricks to make it work, it is purely hit or miss. If they fight the majority of the time you'll end up with a dead aro if not separated. What you do need to have is a way to immediately separate the arowana if things go bad. So most likely you'll need to have two tanks to attempt this, with luck you'll find some taht will co habitat.
Two SA arowana will quickly out grow a 125g tank.
I figured but I do have a question how long will the 125 last them? I do have an extra 100 but that isn't set up I guess I can cycle it now incase things do turn bad. Will the 125 suffice till December? My pond should be done by then. I've try mixing 2 silver before and the result wasn't bad it wasn't perfect. How will the do in a group of 3? And also are they like other fish When it comes to housing them together? I have more experience in mixing cichlid but new to arowana. How are the Arowana mixing compares to cichlids?
Thank everyone for the advice