This encounter heavily depends on location. If BK has an elevated position outside, you need assistance to reliably take him out. He can easily poppy bomb you and himself in opposite directions, knocking you out of range for basics.
Fighting Skye is a lot like a game of Tic-Tac-Toe. Whoever gets the first hit has the advantage. A sky that's hitting headshots can kill a fernando with one magazine. She's squishy, though, so it's easy to turn the tides and make her need to retreat.
Zhin attacks slowly and his third hit in his attack chain is easily his scariest. His first two attacks deal about 450, where the third deals 700. While not taking damage at all is priority, avoiding that last hit is the most important when fighting.
Ruckus is a jack of all trades. He can build more towards damage, support, or tankiness. Either way, his miniguns are contenders in the "Top DPS" market, and any Ruck can deal a surprising amount of damage in a short time. If he ults, just run.