I have found that to label a fish with 100% certainty about its personality is wrong.. there are some red devils that are not aggressive..i have one that is so mean and nasty i cannot compare it to any other fish i have ever had..i have two others that are mellow and sweet.. and they are almost full grown..as a rule devils have aggressive personalities but yours are from the same parents and maybe they took on the same attitude since they were all raised from babies together they may end up excepting each others space.. I have green terrors that live with my african cichlid..the africans are much more aggressive.. so for some these combinations do work..I have a huge oscar and reddevil together..they are buddies..