What build and tactic setup are you using for the AI controlled DW rogues?
Disable caltrops, set Sera to always use Flask of Frost primary. This is up almost every fight, and usually allows her to tank everything for long enough for it to die.
Besides that Cole is set only to use Stealth first, since he is assassin and gets 100% to crit from stealth.
At lower levels, I make sure they both have spinning blades, but later I get twin fangs, and death blow, as well as upgraded flank attack. I pick up first blood from archers tree for multiplicative source of damage increase. I go down and get looked like it hurt, then eventually cheap shot later. This gives pretty much unlimited stamina. As hidden blades and spinning blades both give max stamina on hit/proc. And pretty much just stealth on the stealth tree as I have no need for armour pen with so much sunder.
Of course I use 5x guard to help vs stagger and knockdown, and then 4x hidden blades and x5 hidden blades.
So you use spinning blades, which hits 9 times, and can usually proc multiple hidden blades. You usually get like 9-18 hits. Which all generate guard and stamina. Which allows you to dump all your stamina on twin fangs, flank attack, death blow. And it works out where your spinning blades is back up about that time, which fills stamina back up for a rinse and repeat.
Thats the jist of it I think, pretty effective. You set this up correct on nightmare and you can sit back and watch your party kill everything. You don't really need to help at all , very just BEAST mode everything. It may get boring, as you want get much challenge from anything though.