The two sentences that include errors in the use of possessives and contractions that should be corrected are:
- "We are not certain who's textbooks these are, but we want to find out so that we can return them." (Should be "whose" instead of "who's")
- "Don't forget to pack your coat and hat, because its going to be snowing in Minnesota all week." (Should be "it's" instead of "its")