I would agree with Toby, about another year till it gets to be a real problem, but your rays will appreciate the extra space even now.
Just a side note, you had mentioned breeding, not sure if your aware or not but that 6-7" male is not going to be ready for breeding for a while, probably 6-12 months depending on his growth rate. Usually happens when they are right around 12". Your big female might be ready or close, smaller one probably needs a few more inches.