A couple of additional tidbits to help you with establishing trust … parrotlets cages are their safe zone, their territory where they feel safe. Your arm and hand can look remarkably like a snake coming into the cage so when you go in, keep your hands as low as you can when you’re getting their dishes out, etc. If they approach you, just keep your hand flat. Our hands can look like the gaping maw of a snake to these tiny little prey birds, so keeping it flat is less intimidating…still intimidating but less in the “I’m about to eat you” sense. In theory anyway.
Music is also soothing so you may want to test out some music on them. My girl Kiwi seems to like smooth jazz for some reason. Others do well with nature sounds. Just try some options out on them. My goal for you is to get them more at ease with your presence and to give you opportunity to observe them in a less stressed state. That way, you will be more familiar with their body language and can prevent stress before it gets them flapping around. I mean, not always - as wild birds (despite being raised in a human environment), they will naturally respond to fear by trying to fly away and there are just situations where you have to get your hands in there. I also hope it will help to assess their relationship with each other so you can have some realistic expectations on their interactions with you. Bonded pairs don’t typically have that much interest in their human, but they are all different personalities so you never know. You can also have a very enriching experience with then even if they are not bonded to you. But all in good time. Do you have any particular expectations or hopes with them?