Question about multiple domains and one hosting (seo)

I have three domains and a single (shared) hosting.
Let's name the domains domain1, domain2 and domain3, with domain3 being the one that's already connected to the hosting.
Now each one must be a separate site, appearing so for visitors and searchengines, but all hosted on the same location.
I guess I need to create the subdomains domain1.domain3.tld and domain2.domain3.tld and let the actual domains domain1 and domain2 direct to their subdomains on the domain3 hosting by using a frameset. Will this be seen as individual sites by searchengines, or will it harm the ranking (I know that having multiple domains to the same site is bad). If this is not the good way to do it, then am I forced to have a hosting per domain or is there any other way?