I need to generate a promissory note for a loan between family members. How do I go about that, so that it's legal and binding?

At least have the signatures notarized.

It needs to be specific, as to how much is borrowed, and what the payments are going to be, and when they start, and how many payments are to be made. Also late fees and the such should be noted.

Most office supply stores offer blanks that can be filed in.

Also interest that will be charged, if any.

There should be promissary note forms online too.