There is a rule that says 1/0 is the smallest conductor that can be paralled. I can not quote right now.
That does not apply to EGCs in parallel.
(H) Conductors in Parallel.
(1) General. Aluminum, copper-clad aluminum, or copper
conductors, for each phase, polarity, neutral, or grounded circuit
shall be permitted to be connected in parallel (electrically
joined at both ends) only in sizes 1/0 AWG and larger where
installed in accordance with 310.10(H)(2) through (H)(6).
(5) Equipment Grounding Conductors. Where parallel
equipment grounding conductors are used, they shall be sized
in accordance with 250.122. Sectioned equipment grounding
conductors smaller than 1/0 AWG shall be permitted in multiconductor
cables in accordance with 310.104, provided the
combined circular mil area of the sectioned equipment
grounding conductors in each cable complies with 250.122.