Disk Utility unable to resize partition

I have an external 4 TB drive with two 2 TB partitions, A and B. I want to resize the partitions so that I have one 3 TB partition and one 1 TB partition.

When I try to use the Disk Utility GUI to accomplish this, it shows me I actually have three partitions:

Partition A (2 TB) – "You can not remove the first volume on the disk."

Partition B (2 TB) – "You cannot remove this volume because the previous volume cannot be resized."

Free space (516 MB)

When I try to (in a single action) remove the free space, then remove Partition B, then add a new 1 TB partition and resize Partition A to 3 TB, I get the following error:

"Running operation 1 of 4: Remove “--”…

An internal error has occurred and the disk for one of the specified operations could not be found. This may be a temporary issue, try again.

Operation failed…"

Similarly, when I just try to remove the free space and Partition B, I get the same error (now when "Running operation 1 of 2").

Any suggestions on what I can do? The result of running "diskutil list" with both partitions mounted is shown below. ("Dan's Carbon Copy Clone" is Partition A and "Data Dump" is Partition B, though I am amenable to deleting whichever partition is required as they are currently exact duplicates of each other.) Thanks in advance.

/dev/disk0 (internal, physical):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme            *1.0 TB   disk0

  1:            EFI EFI           209.7 MB  disk0s1

  2:         Apple_APFS Container disk1     920.0 GB  disk0s2

  3:    Microsoft Basic Data BOOTCAMP        80.3 GB  disk0s3

/dev/disk1 (synthesized):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   APFS Container Scheme -           +920.0 GB  disk1

                 Physical Store disk0s2

  1:        APFS Volume Neutrino        730.4 GB  disk1s1

  2:        APFS Volume Preboot         24.0 MB  disk1s2

  3:        APFS Volume Recovery        519.0 MB  disk1s3

  4:        APFS Volume VM           4.3 GB   disk1s4

/dev/disk2 (external, physical):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme            *4.0 TB   disk2

  1:            EFI EFI           209.7 MB  disk2s1

  2:         Apple_HFS Dan's Carbon Copy Clone 2.0 TB   disk2s2

  3:     Apple_CoreStorage Dan's Carbon Copy Clone 2.0 TB   disk2s3

  4:         Apple_Boot Boot OS X        134.2 MB  disk2s4

/dev/disk3 (external, virtual):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:         Apple_HFS Data Dump       +2.0 TB   disk3

                 Logical Volume on disk2s3

                 [disk ID]

                 Unlocked Encrypted