There are a couple of ways you could go about this.
Firstly, to change the navigation bar and remove the site members link, you'll want to override the collaboration-navigation webscript to remove that item from collaboration-navigation.get.html.ftl. I'd be tempted to create a new webscript to replace that one and then create a module to swap those two components.
I know, this is very old message but still in the hope of finding a solution, i am posting this -
Is there a way to hide "Site Members" link Only for the consumers? If thats not possible, is there a way, i can disable the clicking on site members only for the consumers?