All you would need to do us add more meta query value sets. For example adding the following code after the first meta query section should do the trick.
$bathrooms = explode(',', $_GET['bathrooms']);
//Add our meta query to the original meta queries
$meta_query[] = array(
'key' => 'bathrooms',
'value' => $bathrooms,
'compare' => 'IN',
);
Then you can add a bathrooms get param to the URL. Eg http://mysite.com?bedrooms=1&bathrooms=2
