How to allow/not allow subsite owners to edit Pages - edit button

Sorry for bothering you again and again.

I create a few Pages in the default template for subsites. I want to
1. allow subsite owners to Edit 1 Page, but rest pages are not editable for them
2. show an Edit button on the Page that is editable if they logon, of course plus the Pen icon on the top in admin toolbar

Is it possible?

Best regards