Enforcer: this is usually reapers job to handle. though Mcree and Genji may want to flash and stun if they become a problem.
Sniper: Mccree should almost always be on top of snipers. but Genji may help.
Assassin: Genji can dash through. Moira can fade. Mccree can flash. and Reaper can wraith to escape from her. and always stick together
Heavy Assault: the best combo you can do is wraith to bait out charge. deflect. flash and then repeat. you most likely will want the reaper taking the damage if you have too. the tanks on his back count as crit spots.
For the first part of the mission you always want to position reaper on the side of the doors so it is easier to lay damage into the grunts. recommended to not use ultimates in this stage.
when you blast through the doors Reaper and Genji should go right. while Mccree and Moira go left. as i believe this to be most efficient. once the sniper spawns Genji should allow the sniper to target him while Mccree and Reaper close in.
Once you reach the docks Mccree should have high noon. if so use it as the boats come in. Inside the house Genji should focus the top level. The absolute second Reaper can leave the house he should. then he must teleport across the bridge to the balcony behind it and attack the sniper.
Once you get into the area where the assassin appears. Enforcers will come through the doors ahead of you. Reaper should go forward and death blossom them. the ideal situation is where Mccree flashes the assassin and you kill her the first time. Reaper must get his ultimate as quickly as possible.
This is where you will find you first H.A. (Heavy Assault). it is the best if you can execute the combo listed above. if not then Reaper should soak most of the bullets while Mccree high noons and Moira heals him.
Once you hit the large circular room. Reaper must ult the grunts in the middle while they fall down in order to make room for the assassin. again the ideal attack would be Mccree flashes her and she dies instantly.
(All directions from here on out are placed as if you are on the high groun looking at the door from which you came)
The attacks are random now as you never know which ones you wil get. if they come in by boat then Mccree high noon is the best option. if it is the door to your left were all the enforcers come out. the Genji should dragonblade while Moira ults to heal him. you want to position yourself on the high ground for the most part.
once you kill the last H.A. run as fast as possible to where the ship picks you up. if you need extra points you can kill soldiers on the left of you before the H.A. comes up the stairs.
Now i am by no means a pro. but i hope my guide helps anybody who wishes to complete this gamemode on the harder difficulties. if i get enough positive feedback i might make one like this for uprising.