Buy a lot of strength tomes, so you have a bit extra health. Get skadi rapier to have magic resistance. Heart of tarrasque gives you enough health regen to live through the poison, and only one or two of the like five types of poison resets the heart cooldown, and it is short compared to the others.
Octarine core and stormbearer together gives enough healing from spell lifesteal that you can survive while fighting the dragons as well as manage to kill them through the omniknight ult.
Get a refresher orb as well, that way if you do die, you will have an extra life with the rapier, and a third life by refreshing the rapier. Also refresher has a shorter cooldown than the rapier. When the round is about to end (when just an omniknight or something is left) try to wait it out so that you have your rapier and refresher off cooldown and no active poisons, as otherwise the poisons will leave you at half health when you need to fight the bears.

it doesn't go through bkb only the slow does

Thx for the tip with heart, it heals around 400 hp/sec :D And yes, it does not go through bkb. I guess I died from those who do. And attacking seperate spawns helps a lot too ^^

The next 2 waves are easy peasy =)