As Barik, drop your Turrets and shield, play a cat and mouse game where youre the mouse, let the turrets do damage meanwhile and keep your shield or cover between you and the turtle.
If you suspect Mal'Damba has his ult ready, try to space yourself a bit from the rest of your team. Dread Serpent will knock you out of the air if you're flying, and its hitbox persists for a few seconds after it triggers.
Makoas LOVE to flank healers, and he can deal a lot of damage to you. Your best bet is to use Agony, and stun him whenever he comes after you. This will give you a good chance to run away or ask for help from your teammates.