Tonight my brother, in heavy boots, is walking through bare rooms over my head, (1-2)
We're introduced to our speaker in the words "my head," but he's basically out of sight otherwise. These lines are all about his brother. In fact, the speaker simply acts as a reference point for where his brother is (upstairs). Right away this establishes that, in their relationship, our speaker puts his relatives first. He's more of an afterthought.
My father keeps a light on by our bed and readies for our journey. (12-13)
The poem changes scenes but remains firmly focused on family, turning now to the speaker's father. Even though our speaker uses the word "my" again, it's really all about who he is in relation to his father. He's included in that word "our," and portraying himself as part of that first person plural is a way of stressing that he's a part of a bigger, more important unit (the family). At this point of the poem, he doesn't seem like much of an individual.
He mends ten holes in the knees of five pairs of boy's pants. (14-15)
Aw, that's sweet. Papa is totally taking care of his kids here, and by sewing no less. What's so great about this description is that not only does it tell us how much the speaker's dad loved his sons, but it also tells us just how much the speaker respects his old man in return. He's acknowledging all the hard work his dad put in to look after his youngsters. No wonder our speaker seems so torn up about his death.
God, that old furnace, keeps talking with his mouth of teeth, (23-24)
Because of the way this poem has established a sort of structure, God falls in the same place where our speaker's brother and father were before. God's like the super father, the patriarch, the guy at the tippy-top of the family tree. Add on top of this the familiarity of the phrase "that old furnace," and we get a strong sense that the relationship between our speaker and God is in many ways similar, or parallel, to a family relationship.