A document can have only one template at a time. Word is a complex program and the task you describe brings out some of its hairier complexities.

You can create a document based on each of the templates and cut and paste to put elements you want into each.

Be careful of mixing styles.

If you want headers/footers (not headings) to be different in different parts, you will need section breaks.

Start here.
Basic Concepts of Microsoft Word - from Shauna Kelly
For more on sections and section breaks, see:
Sections / Headers and Footers in Microsoft Word 2007-2013
For more on Styles see:
Understanding Styles in Microsoft Word