I do not understand what you were trying in your examples -- I think maybe you are muddled about how $sanitizer works? All it does it return the sanitized value.
All you need to do is this:
$activepost = $sanitizer->selectorValue($page->title);
$articles = $pages->find("template=post, cbpage2=$author, limit=2, title!=$activepost, sort=-cbdate" );
/**
* OR: in case you need to use it unsanitized elsewhere
*/
$activepost = $page->title;
// note the position of the sanitizer method
$articles = $pages->find("template=post, cbpage2=$author, limit=2, title!=" . $sanitizer->selectorValue($activepost) . ", sort=-cbdate" );
/**
* OR (again): if $activepost is only used in the selector, you can ditch it altogether and use $page->title directly
*/
$articles = $pages->find("template=post, cbpage2=$author, limit=2, title!=" . $sanitizer->selectorValue($page->title) . ", sort=-cbdate" );
*/