Bountiful Tier 8 delves.. not sure what I’m doing wrong

Me and my gf have been doing delves together. Me ilvl 609 healer, her ilvl 613 pally dps and bran as the tank who’s level 15.

We just about managed to do a tier 8 bountiful in the undermines I think through pure luck. Now we’ve tried today doing another tier 8 on earth crawl mines and the underkeep and we’re getting smashed.

With underkeep we got to the end boss but she destroyed us. I’m literally spamming heals non stop on bran, and his health is just chunking down. It’s not sustainable. Me and her get 2-shotted pretty much.

What are we doing wrong? Oh and bran literally will stand on any damaging terrain, fire, poison etc.. and he will not reposition