When Ronny mentions dad’s death, Phillip quickly dismisses it as an accident that happened in the spur of the moment.

PS: Ronny and Phillip contributed to dad’s death.

Here if dad is the father, it should not be capitalized. If it refers to a person’s name, it should be capitalized.

” I wish we had not asked dad where all the other lemmings in Lemmingville had gone to all of a sudden.”

Phillip replied:

” Yeah bro, and I wish I hadn’t asked him if had any plans for the afternoon, but what the hell, it was an accident, who could have known he would act so impulsively?”.

I didn’t see problems other than it being “an accident” not “a accident.”

EDIT: regarding the tense, if this is a book report talking about how things happen in the story, the present tense is fine.