Disregarding tank size, I've placed two males (2 pairs) in my tank and they seem to fight. it didn't work well for me and i had to sell one. i now have 1Male and 2Female.
7x2x2 is a 210g. Whats the dimensions of your 450? It is an 11 inch ray you are looking at, which is already known to be sexually aggressive. It's a bad idea for you to attempt to add this ray to your system unless you have a mature female. Try to raise your pups up to maturity. It shouldn't take long. No sense in jumping in over your head.