Does SSL need dedicated IP

Hi,
If in my reseller account, I have 3 customers who need SSL, does that mean each of these three need a dedicated IP? Or can they all share the same IP?
Or, can I install 1 SSL cert and all three customers can share this 1 cert?
Very confused about how all this works, never used them before.
Secondly, What is the easiest way to resell SSL cert to my customers? I use whmcs. Is there a plugin for this (like the domain name module) where all the setup and purchase can be automated?
Thanks for helping my noob questions