Hello, @tom.
Unfortunately, it is not possible to use all the features of the theme without activating it. You must activate the theme first, and then you will be able to install the theme plugins and import the theme demos.
We do not suggest installing the theme on a site that already has another theme installed, as this may cause unexpected issues. We always recommend installing the theme on a fresh WordPress installation.
Please watch and follow the instructions in the video linked below:
https://www.youtube.com/watch?v=i7STFGZapx8&list=PLMqMSqDgPNmCCyem_z9l2ZJ1owQUaFCE3&index=2
Best regards,
8Themes Team.