"My father is dead." It's the first time I've said it since I told Tobias, on the train ride over, that my parents died for me. "Died" was just a fact to me then, detached from emotion. But "dead," mingling with the churning and bubbling noises in this room, strikes a blow like a hammer to my chest, and the monster of grief awakens, clawing at my eyes and throat. (5.15)
Strangely, it's changing death from a verb (died) to a noun (dead) that really hits it home for Tris. We guess that, as a Dauntless, she's used to action, action, action, and dying would be just another action for her.
Years from now, when my memories begin to fade, what will I have to remind me of what [my parents] looked like? (7.49)
Almost everyone fears they'll forget someone after that person dies. Many people have pictures or videos to remind them of their loved ones. Tris, however, having grown up in Abnegation, doesn't have these things. She has only her memories to rely on, and as we've seen in these books so far, memories are malleable and easily changed or forgotten. She doesn't want to lose her parents forever.
I don't know how I expected him to say [that his father was dead]—with relief, maybe, because Marcus, his father and the menace of his life, is finally gone. Or with pain and sadness, because his father might have been killed, and sometimes grief doesn't make much sense. But he says it like it's just a fact, like the direction we're moving or the time of day. (7.156)
Tris is strangely critical of how Tobias chooses to mourn (or not mourn) his father's presumed death. She seems to forget that just seven chapters ago she had no reaction at all to her own parents dying… and she actually liked them.
"Don't be an idiot!" [Fernando] says, his voice weak. "Leave me." (42.65)
Fernando goes against what is expected of his faction, Erudite, by being so brave in the face of death. By sacrificing himself, he acts more Dauntless than Erudite, don't you think?