Throughout the story sometimes grandma and grandpa are capitalized and sometimes are not capitallized. how come?

Grandma and grandpa can be a general term like the grandpa was walking. In the cases when it is capitalized, grandma or grandpa is being used as a name like, "Hey Grandma, can we go to the store?" an example of non capitalized words would be, "my grandma is very kind." Hope this helped!

Terms like grandma and grandpa are capitalized when they are used as titles that refer to someone or something, rather than a regular common noun.
For example, if you were to say, "Let's go to Grandma's house," then that would be capitalized because you are referring to your grandmother with a title, instead of saying "Let's go to my grandma's house," where you are simply stating a noun. 
In short, think of titles like names. It's kind of like saying "boy" v.s. "Adam" if you think about it. Hope this helped!

Is it for you because if it is it's not a surprise

Are there any answers