If you are planning to write and publish a family history yourself, your word processing software not only has the tools to help you write and edit your project but assist in the design and construction necessary to construct a "press-ready" publication. Here's an overview of those tools. Now it's up to you to learn how to make them work for you.
In today's world, underlining is for hyperlinks, not your publications. Use italics to emphasize text, not underlines.
There are many great outlining applications available to help you pull your writing project together, but before you begin hunting take a look at your word processing software first.