if you set a trigger to do MPC (multiple parallel conversions), means you set more ADCSELx bits in TRGCFG then subsequent n items in your list specifies channels parallelly converted. So second option you outlined is correct
if you set a trigger to do MPC (multiple parallel conversions), means you set more ADCSELx bits in TRGCFG then subsequent n items in your list specifies channels parallelly converted. So second option you outlined is correct