Multisite htaccess and user-friendly redirects

I have WP Multisite running within an existing site that has a lot of html pages including index.html as the main home page. The intention is to retain a large amount of non-wp content in a number of subdirectories, and add several wp sites in addition so parts of a large site will be wp and other parts non-wp so that editing parts of the site can be delegated to colleagues who don’t write html. We are currently working on the first wp site.

The problem I am trying to solve is an .htaccess problem. The current wp part of this is:

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]

RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule ^(wp-(content|admin|includes).*) picture-shop/$1 [L]
RewriteRule ^(.*\.php)$ picture-shop/$1 [L]
#Removing the line below makes intra-site quick links work but not full url redirects
#removing the line below causes wp viewing to fail
RewriteRule . index.php [L]

Now this works OK for wp. But earlier in the .htaccess file I have a long list of simple redirects that provide for user-friendly URLs so the user can type https://www.canalmuseum.org.uk/groups and this redirects to https://www.canalmuseum.org.uk/visit/groups.htm

The code is

RewriteEngine on
RewriteRule ^groups$ /visit/groups.htm [r=301]

and this comes at the beginning of the .htaccess file.

There is a conflict between these. The wp section redirects any phantom URL to index.php and the result is a 404 error using the wp 404 page. If the URL to which the user is supposed to be redirected is a complete URL I get a 301 moved permanently error.

I want my cake and to eat it here, I want the html part of the site and my user-friendly redirects to function as if wo did not exist, but equally I want wp pages to work, which they don’t if RewriteRule . index.php [L] is removed.

I wonder if anyone can suggest a way to make them both work?