Answer:
1)Maybe he and I will go to Spain together.
2)Mine
3)Whom stopped to pay attention to the street performer?
4)Who is this package for?
5)Show ownership
6)I
7)He himself wrote the 20-page paper.
8)Him and me worked together on our community service project.
9)They are surrounded by commas to set them apart from the sentence.
10)They