notes lenght

please post part of a score that shows us what you are wanting to do.

Notes with different lengths on the same beat must be in a different voice. So select the note, set it to voice 2, 3 or 4 and change its duration.

If you copy notes from a voice 1 source they are pasted in voice 1 and will overwrite existing notes.
So exchange voice 1 & 2 either in the source or in the destination befor C&P. Afterwords change them back if necessary.
Another option: temporarily add the same instrument again directly below and insert the notes there. Then select both staves and use Implode. These notes are then added to the line above as part 2.
The temporary instrument can then be deleted.