So you do that and then this then that and then I get free points
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In the first sentence, the "he" is a nominative as it is a subject.
In the second sentence it is an object as the form "me" is actually "I", but "i" is a nominative form and "me" is an objective form.
In the third sentence "Us" is also used in objective form as "us" is an object of an action by "my sister".