It wouldn't be OK for a long term set-up. As juvies they'll be ok until the cons start breeding, which may be sooner than you think (they could be expressing courting behaviour already!
).
You could keep the juvie JD's and let two of them pair up and keep the single pair in the tank, you can have a pair (possibly 2) of cons, or you can have both species but all would have to be the same gender.
OR you can ditch both cons and JDs and look for something different to suit your taste.
Though they don't get very large, cons can be very territorial and aggressive when spawning but watching them spawn, brood, and raise their young is an experience that really shouldn't be missed. So...the choice is yours. What you gonna choose?