If they're not interested in being aggressive towards eachother unless they're "protecting" their cages or whatever, I don't think a neutral introduction would be too bad right now.
Your plans on introducing them sounds just fine to me, that's pretty much what I did with Miley and Alaska.
I however really don't think you should clip Charlie, and especially if he's the more "aggressive" one, because if Merlin would try to be close to Charlie, and Charlie didn't approve, and also felt like he was limited and couldn't really get away/fly as well as before, that would more likely just increase his "reasons" to attack. If he doesn't want Merlin close, he'll probably just fly away, I don't think he would actually attack Merlin without a real reason, since it doesn't sound like he's been paying Merlin too much negative attention before.
My Miley have been known to attack me for.. Moving my head a bit too fast for her liking, or.. Just seemingly without any reason at all, so she's definitely my more aggressive bird.
Before she and Alaska got along, Alaska seemed to like her way more than she liked Alaska, which lead to Miley feeling a bit annoyed with Alaska's constant following her around. More often than not, Miley would just fly to me or the tree to get away from Alaska, and Alaska would often leave it for a while. If she did fly after her, or if Miley felt like she had no way of getting away, she would kind of raise her wings, open her beak and almost "threaten" Alaska (like in
this photo, from their actual first meeting!), but never actually bite or attack.
This was SO SCARY for ME in the beginning, but as Alaska learned to respect Miley's privacy and recognize these "warnings", I also learned that they were nothing but warnings.
In the beginning, after these warnings, Alaska would find herself a bit startled, enough for Miley to find an opportunity to fly away from her instead.
I feel like if Miley had been clipped during these events, she would've probably been frustrated that she couldn't really get away as well or as fast, and since Alaska didn't really get the warnings straight away, I'm afraid that all might have lead to some bites or attacks.
So yeah, I definitely recommend to at LEAST try it out without any clipping involved. Just watch their body languages carefully. Try and learn and look out for the difference between harmless warnings and potential attacks.
Also, I don't know what other people did/would have done, but when I introduced my two, I had in mind not to interfere too much, but rather let them fly away or come to me on their own. Because I feel like, if I would have removed Alaska when Miley was warning her, Alaska wouldn't have learned what Miley tried to say, or that it WAS a warning - and if I would have removed Miley, she would have been REALLY OFFENDED that I only picked
her up when
Alaska was being a pain in the butt.
So yeah, I'd let them do what they wanted to as long as they didn't show any real aggressions towards eachother or anything.
Of course, I only had them out together for a little while at a time in the beginning, so they didn't have to deal with eachother too much and both got their own time with me too. (After a while I started having them out together for longer and longer, since when Miley was with me, Alaska kept away, and vice versa - so giving them private time with me worked just fine with both of them out in the birdroom too, and when they felt like it, they could interact with eachother too. ...Except they didn't really care about eachother until after 2-3 months or so of that, haha.)
I hope my experiences can be of any sort of help, and I REALLY hope your boys will do just as well as my girls.... Or better!
So he had a little trouble moving around, he headed over to the plank and tried to climb up. Andrew wondered why he didn't fly, I presume he didn't want to draw too much attention to himself. We let them both do their own thing on the bed and just watched (we had tea towels at the ready!).
