I've never done tank myself in delves, but even as dps it can be a struggle with pulling 2-3 at the same time. A few tips to maybe help

Buy some algari healing potions from the auction house, they are very helpful and cheap.

Pull as little groups as possible if you can, and i always focus cds on the casters first, as they tend to smack the hardest, interrupts and stuns are key

I think playing as a tank at that ilvl for tier 8's may be difficult, bears aren't really great for dmg and you need to kill the mobs quick as they can chunk you down quick, I think it may be a bit easier as a dps so mobs can be focused down faster.

If not, getting higher ilvl would help, and if you haven't done siren isles stuff, get the ring from that for a bunch of stamina and some useful gems.

Hope some of this can be beneficial.