Transfers

A transfer in Quicken is between two accounts in the same file.

What you have described is not a Quicken transfer, so they are just credits & debits using some category(s) of your choosing, but there is no knowledge shared between the files via Quicken. Each movement of funds will require two transactions, one in each file affected.

You might want to create categories like A_to-from_B, A_to-from_C, A_to-from_D, etc to make all the possible combinations.

Not sure why you created a separate file for each checking account, but I hope it was for a good reason as it is making more work for you.