Parrotlets sure are fearless little featherballs. Twitter might be afraid sometimes if he sits on my shoulder and I go down to the basement, but that's only because I used that trick several times to get him to a dark room and catch him when he refused to bath... Now I found another way to catch him so the basement is not that scary anymore, still I feel him tense but he keeps his ground, you don't think a stupid basement is enough to scare him, right?! He wouldn't go on his own, but on my shoulder it is safe and he can do anything. Also when I use the vacuum cleaner, he was scared first but came back because curiosity is always stronger. Now he doesn't care anymore, the vacuum cleaner is just a noisy beast.
You are very right in that you should never let your parrotlet unsupervised with your other birds. And having other birds entering a parrotlet's cage is an appeal to crime. Budgie Merlin nearly lost a foot when he tried it. He was bleeding quite badly and was shocked for a good while, but he didn't learn the lesson. Several times after that he would try and land on Twitter's cage, so I kept it closed when all the birds were out. Now Merlin has a new friend so he doesn't care about Twitter and his cage, no one tries to enter there anymore and it can stand open again. But they are never left together on their own. They can fly together if one of us is in the room with them but as soon as he is being a bad boy, Twitter is back in the kitchen in detention (I don't have a door to the kitchen but a mosquito net-curtain does the trick). Never trust a parrotlet...
As for cuddles, Twitter would sit on my finger in the late afternoon and sleep while I type. I can then approach a finger and offer to scratch him. To do that I present my finger slowly a little aside his neck and wait. If he wants cuddle he would open his beak and kind of gently lick the tip, then offer his neck or the side of his beak. So I can scratch him, or stroke, or he uses my finger to do it himself. Only around the neck and on the head, he won't let me touch him anywhere else and I read that only lovers are allowed to touch other parts of a bird's body so that's fair enough. I wouldn't want to give him the wrong impression and leave him frustrated!!
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