Here's our current Scrum board view (from one of the columns), swimlines are set by assignees:

I'm trying to sort between the 2 stories on the board while the story is assigned to someone else (multiple sub tasks to multiple assignees on the same stories) but it doesn't work.
if the story was assigned to the same assignee, you can drop & drop them but not when the story is assigned to someone else.
Is there's anyway to sort them on the column without using priorities instead for rank?