Success! I ran the Keeper of Rainbow dungeon earlier today and was slaughtered, but I had taken a resolve team. I waited for my stamina to replenish and then tried the Keeper of Fire dungeon...but forgot to change my team so I was slaughtered again. I used one of the eggs they sent me to get my stamina back and went in again, but I went back to my standard team (D'Spinas, Tyrannos, WMWAsgard, Angel, Lilith). I died again. Waited for my stamina to come back and tried one more time, though this time I changed out Angel for a Fire Golem and took a friend's Angel. It took a while, but I finally beat the Keeper of Fire dungeon and got both the Dark Keeper and the Fire Keeper I needed!
I went ahead and evolved my D'Spinas but now I don't have any more team points to spare so I can't evolve Tyrannos yet (he's close, like less than 10 levels to max). I may run the fire dungeon one more time today to get some more food for Tyrannos and hope I get a team point increase at level 41.
EDIT: I meant to ask. Would it make sense to put Angel as my leader, have D'Spinas, WMWAsgard, and Tyrannos in the team, switch out Lilith for a golem type, then use a heavy hitter type from a friend?