It's funny, we started the faerie drakes at Int 14, but they were listed as low to average in the original text. These are average to high, so start at 16? I could also see somewhat higher Wis and less Dex. Sure.
Skipping ahead to the breath weapon (can I anticipate this already?), we can use just the weaker version and say that it can apply a (enlarging metabreath) feat to it 4/day.
These are slightly bigger than faerie drakes. Allow them to reach Small at young adult? If so, improve Str and reduce Dex as usual for the size increase?
Hmmm...I fear we may have gone a bit overboard with the last one. Its intelligence was supposed to be worse than this one, which if we go with the proposed increase, will eclipse the red dragon.
By 2e scores, the demon drake should more closely follow the copper or brass dragon's mental ability score progressions.
Then dumb it down a bit. Really won't kill this thing much. We can always go back and RetCon the faerie drake if it's a bit too overpowered. That's the beauty of not being bound to a published medium
Faerie drakes don't have frightful presence, so that helps a little, but they do have a Cha bonus to AC ability. I guess that's a wash. I think we should probably reduce the progression for the faerie drake mental scores based on the demon drake description. Maybe we could just reduce them all by a fixed amount at all age categories. Then adjust the ACs appropriately. Simple enough?