Thank you for writing in, regretfully you can only import one demo per site. see the following link for more details.
Setup - Demo Content
You could import demo one at a time and then save the page as Content Template, that way you can load that template into your page regardless of your base demo. However, the looks of the template will not exactly the same because the Integrity and Icon is different stack.
My advice is to Import only one demo, and just replicate the section you liked on the other.