I have not seen corruption like this on gpt. Usually the gpt tools do not let you do this. Overlap issues can be a real issue as you may have written data from both and then have corruption. best is to delete sda5 if possible and it has no data. But you may need chkdsk on NTFS and fsck on ext4 partitions afterwards.
Best to have good backups before doing anything.
/dev/sda5 overlaps with /dev/sda7
/dev/sda5 overlaps with /dev/sda8
/dev/sda5 overlaps with /dev/sda9
And the errors you are getting are from booting in BIOS mode from sdb which has a very old grub legacy boot loader in the MBR.
You only have UEFI installs, so should not be booting in BIOS mode.
Edit: Be very careful that drive is really still sdb, but since UEFI erasing sda should not matter.
Zero out MBR only of sdb Use bs=440 if windows as serial number (BIOS only) is between 440 & 446.
dd if=/dev/zero of=/dev/sdb bs=446 count=1
see also this: