We definitely want members of the subsite to access the parent site, but not necessarily the other way round. Is this easy to do?
2 Answers
Yes it is possible, the sub-site has its own Permissions and you can setup its unique permissions so that the users you want have access to sub-site [not all of them]
You simply need to play with Site Settings -> Permissions when in sub-site!
Yes, you have to break role inherticance in subsites
with powershell here: http://marcboes.wordpress.com/2011/03/02/break-inheritance-for-sub-sites-and-remove-visitor-role/
with the GUI I guess its possible as well.