Hi nemerleb. Sorry for the late response but better late than never, right?
FOR brother are thou last?
Scratch your head while hiding behind the brother
Have the brother and sister stay at the same position (By default, the girl is standing behind the boy). Then while the girl is selected, wait for a few seconds until its second idle is played(which involves scratching her head)
Fly like a butterfly
Fell from a height of 2 blocks without touching the ground
Fall from a height of 4 blocks without touching the ground
For both of these, jump from a ledge, then while in-air, zoom out, and bring a map pieces which will join at the bottom perfectly. Then let the character fall more, then while in-air, again zoom out, and again bring a pieces at the bottom which fits. So do that until u get this achievement while remaining in-air. (Note, this cannot be done on any level. Only on some specific level e.g. on Level 2-4 )