1)
Review usage of これ/この, as Mike-san wrote for sentence 6.
4)
Use katakana for Mary.
4) 5)
それ can't be used when referring to a person who is really there. It's valid when, for instance, the addressee is referring to a person in a picture. あれ can be used for your in-group members(e.g. family members). あの人 is more appropriate for out-group members since あれ could sound rude.
As for the difference among こ, そ and あ, see the following thread.
Kore/Kono, Sore/Sono and Are/Ano
So, what is your corrected translations?