How to allow specific people access to a website that is in maintenance mode

I am using the plugin ‘WP Maintenance Mode’. Latest version and the latest version of WP.

I need to do some major work on the site, but like to have selected others have a look at the site as it would eventually appear when the plugin is turned of. These ‘others’ would only need aces to the site, as it would look like to a visitor, when finished. But not be able to do any maintenance or see all the code etc. like I see as a admin.

Can this be done easily? A kind of ‘membership’ plugin? Of course it will need some sort of login with password (at least that is what I think). And if so how?

Thanks