This is a strong piece of work. While the subject matter is intense and a bit daunting, it is told with the skill of a master storyteller. The ability to harness powerful emotion to fuel the story without letting it overwhelm the narrative is hard to do. Telling the story as a series of interconnected vignettes is a great way to move things along without letting it get overwhelming or dry. I enjoyed the light tone which balanced out the deeply troubling moments. If this is a sampling of your work I hope you have the opportunity to write the other books you say you hope to write.
Read the story now
As a critique there are two points only I wish to address:
1. It seems there is some redundancy between chapter 7 and chapter 9 as some of the description repeats itself. It also seems odd to describe the shack to a certain extent while speaking of your grandmother, then to discuss your grandfather, then to return to the shack. Perhaps rearranging the order of the chapters may help with the flow. An example would be having chapter 9 right after chapter 7 as a continuation as they really are the continuation of the same thought.
2. Regarding the choice of narration in the present tense in the first chapter, it is extremely effective in bringing an extra level of closeness to the whole scene. I noticed that you only use it for this one instance and wondered if this was calculated or a slip. As you seem to be a very capable writer, and as the positioning in the story works well as a hook, I assume this was intentioned. However, I also know from writing these sort of traumatic experiences that sometimes the present is just how the words come out, so I just wanted to mention it in case it was not intentioned. But as I said, it works well either way.