Ok, so, update.
I received two more Dual r3 over the weekend, (its funny how an order from iTead can take over 2 months for the first two to arrive, then only a few days for the second order to arrive). I again attempted to flash via the Windows esp-flasher app, and again it failed with the exact same errors. I then went out an purchased a new micrSD card so i can build a fresh raspberry pi install and noticed an issue from my original parameters. Where i had esptool.py --chip esp32 --port /dev/ttyAMA0...., i should have had esptool.py --chip esp32 --port /dev/ttyS0.... I ran it with the revised parameters
esptool.py --chip esp32 --port /dev/ttyS0 --baud 921600 --before default_reset --after hard_reset write_flash -z --flash_mode dout --flash_freq 40m --flash_size detect 0x1000 bootloader_dout_40m.bin 0x8000 partitions.bin 0xe000 boot_app0.bin 0x10000 tasmota32.bin
and successfully flashed one unit. I tried this with the original two units, but i think i cooked those. I will flash my last unit later tonight.
Thanks for the assistance.
Hope this helps others stuck in the same situation.