I have structure of website like this:

domain.com/      - main site based on bootstrap HTML
domain.com/blog/ - wordpress blog site

Right now I need second blog based on the same theme and plugins – so multisite wordpress is the best option. However I need new blog on subdirecory domain.com/new-blog/ – so final result should be like this:

domain.com/      - main site based on bootstrap HTML
                 - wordpress multisite main instalation
domain.com/blog/ - wordpress blog site (main site)
domain.com/new-blog/ - wordpress second blog site

Problem of this is common for a lot of people… However I canot find full solution for this.

First

The site domain.com/blog/has homepage in main directory so is domain.com/index.php but I need it on domain.com/blog/index.php. Anyone has idea how to change this?

Second

In main directory domain.com/ I need put some static HTML files and subfolders. This needs changes in .htaccess and add rules for all subdirecory

RewriteRule ….

Also is it ok to put domain.com/index.html in folder where is wordpress?

Maybe is another solution? Maybe somehow is possible to build website like this:

domain.com/index.html      - main site based on bootstrap HTML
domain.com/abc.html 
domain.com/ab2.html 
domain.com/ab3.html  
...                   
domain.com/blog/ - wordpress blog site (main site) - multisite wordpress
domain.com/new-blog/ - wordpress second blog site

Thanks for any help.