Boot Camp Assistant says I need 64 bit iso file

The MD5sum is incorrect. Your ISO seems to be corrupted during download.

The MD5sum should be 

MD5 (Win10_1803_English_x64.iso) = 986e2e17cf6b0b49141cd15699768e6e

Can you post the MD5sum of the ISO?

Can you post the output of

diskutil list

from macOS Terminal.

Can you post the output of

sudo fsck_apfs -n -l /dev/rdisk1

As a test, create a FAT partition using Disk Utility, of the size you want Windows to be, and report any errors.

Start up your Mac in single-user mode or verbose mode - Apple Support and run

fsck_apfs -s -o -y /dev/rdisk1

If you get any errors, see the footnote under step 6.

Boot normally, and run

sudo fsck_apfs -n -l /dev/rdisk1

for verification. You should not see any of the errors you saw earlier.

Try 41GB for Windows. The 121GB disks are now too small to manage both OSes.

You can now remove the 41GB FAT partition, and try the same size using BC Assistant.

Can you post the MD5sum of the W10 ISO?

as in the single user mode procedure?

Yes.

I seem to get the same error again when I run sudo fsck_apfs -n -l /dev/rdisk1 in terminal

Do you see the same exact error message after running the Single-User mode steps a second time?

hmm now i got this, same error but different numbers

warning: apfs_num_other_fsobjects (57) is not valid (59)

Fix apfs_num_other_fsobjects (oid 0x403, xid 0x2ee6e1)? NO

Is this after a second attempt at the fix? The 'NO' indicates that a 'fix' was not attempted.