Riot's color is grey, not dark bkue, and i think the director said he was going to be much larger than Venom, so i believe that should help tell them apart.. But yeah, i 'd have prefered they chose another one of the Life Foundatin symbiotes as the main antagonist like Phage or Lasher since they are more different than Venom.
I dont know if were getting all five, but we see a yellow symbiote in the containment that's proabably Scream, and the woman in the trailer, the one that shoot spikes is has a blueish symbiote so she could very wel be Agony