If your code works, then that indicates that the Options +FollowSymLinks setting has already been made in the server config file httpd.conf or conf.d. Therefore it is not necessary to repeat this directive.
The Options +FollowSymLinks setting has nothing to do with whether search engines will index the old domain names. If these domains are hosted in separate 'accounts' -- each with their own Web root (home page) directory, then you can add a robots.txt file to each Web root directory to stop SE indexing.
However, you may wish to consider using 301-Moved Permanently redirects to redirect each of the old domains to the new domain instead. These redirects should handle all variants of the old domain names -- for example, www.olddomain.com and olddomain.com -- at a minimum.
You should also pick either the www subdomain or the main (non-www) domain of your new domain as your canonical domain name, and redirect from the non-canonical version to the canonical version. In other words, pick newdomain.com or www.newdomain.com, and redirect all other domains to that one.
Having done that, make sure that you link only to the canonical domain -- Do not link to the non-canonical domains after redirecting them. Where possible, ask other webmasters to correct their links to your site if they are linking to a non-canonical domain variation.
You may also wish to redirect non-canonical page URLs to their canonical URLs. For example, 301-redirect "/index.html" to "/".
The goal in all cases is that each page on your site should have one URL and one URL only; all other possible variations should redirect to that one URL. This avoids problems with "duplicate content" in the search engines.