I have created a site that has several sub sites off it. eg group 1. group 2. group 3. When a user from group 3 logs in all he see's is group 3 site and group 2 user only see's group 2's site etc. But All 3 groups share certain documents, wiki sites etc. Is it possible to share these with all 3 sites but only having to maintain in the 1 site. eg I upload a document once and all 3 sites have access to it. Instead of having to upload the document 3 times to all 3 sites.
Which version of SharePoint are you using? sharepoint-15 isn't a valid version.
There are a few ways you can handle this. You can include the shared content at the top level site or a shared site that all three have access to and then use a Content Query Web Part (CQWP) or DataView Web Part (DVWP) to display the content on the sub-sites.