When do you use "will" to make an offer or request?

1) Will you have a sandwich?
Will you do me a favour?
2) Will you want me to (is not possible)
3) I need other examples.
4) Will you have your children picked up from school(is not possible)

In #1, I'd use "will" because I'm expecting positive answers. For improbabilities or impossibilities or unknowns responses, I'd use "would."

http://grammar.ccc.commnet.edu/grammar/auxiliary.htm#would