I see your characters are all 28 or below. You really need to be at 28 or higher for the nightfall. Best option is to do sunsinger warlock to get the self-rez perk to increase your odds of finishing without dying. They are not impossible to solo, just not easy. They get a little bit easier at level 29 but they are still difficult solo.
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My Warlock is the most developed, he can hit 29. I agree that Fireborn is invaluable in this mode. I was playing my much less developed Titan the evening I got clobbered, but I had taken him through Nightfall missions before.