Assuming silver arowanas, this could only work for a short time if they do not fight. Keeping a pair is a crap shoot and a trio doesn't increase odds that much.
With proper care silver aros grow to about 2 feet long within the first 18 months. The aros are going to require a tank that is 8 foot long and 3 foot wide. The 125 gallon will become too small once they are only about 15" long. So your only looking at about 6 to 8 months before needing a larger tank.