1) Since no different tenses were used, we'll have to assume all sentences refer to the same moment in time. If I'm in a position to overtake the second person, I must be third.
2) The last person can't be ahead of me, otherwise he/she wouldn't be the last person. Neither can he/she be behind me, otherwise I wouldn't be in a position to overtake him/her. I'm tied for last place.
3) I don't get how anyone can miscalculate this.
4) We can't be sure Mary's not a guy, it's a boys' name in some languages. In fact, I'm going to assume he is, because otherwise this question would probably have started "Mary's father has four more daughters". Assuming Mary is a guy, I'll have to guess the name of his father's fifth daughter. Since I already know he's very unimaginative when it comes to naming daughters, I'll guess Nunu.
5) I've known some blind people. He's probably not going to ask for them, he'll have someone with him to choose them, to make sure he won't look like an idiot with whatever the shopkeeper offers him.