adult with juvies?

I was at my lfs yesterday and seen this gold severum that i would like to get. The thing is i have two turqouise Severum juvies already in a 45Hgal, i know one is a female not sure on the other one. Was told it was male at pet smart when i bought him a week ago but it is starting to look like the female more and more. The Gold severum is not full grown but twice the size of my juvies. Do you guys think it will be ok. Eventually i will have the 125 ready for a community of sev's. That is the goal.
The picture is the severum in question, is it a male?

Here is the female.

I know this is the female.

If i buy the gold sev what would be the best way to introduce him to the tank? oh yea that convict you see in pic is no longer in there i put hime back in my 55gal.