Multiple sites Vs Miltisite

I’ve been reading up on Multisite and not sure if its the right way to go.

I have multiple WordPress websites installed and successfully running on different domain names each pointing at a sub-directory, e.g.

• Website A = domainname1 = /root/a
• Website B = domainname2 = /root/b
• Website C = domainname3 = /root/c

I’d now like to change the website URLs to the following, so that all websites use the same domain name but still have a different sub-directory:

• Website A = domainname1 = /root/a (no change required here)
• Website B = domainname1/b = /root/b (same directory as before, but with different website address)
• Website C = domainname1/c = /root/c (same directory as before, but with different website address)

The closest I’ve come to getting this working:

• Set the WordPress Address (URL) to subdomain.domainname1
• Set the Site Address (URL) to domainname1/b
• The site loads fine as long as I go to a page using the sub-domain; as soon as I click any links on the page I get correctly taken to the URL I want but see a 404 error

Any help will be gratefully received.