Have CSS Class Added with `is_page()` WP function

Bitwise operators expect conditionals on either side of them to evaluate to either TRUE or FALSE. If FALSE it checks the next conditional until it finds a TRUE or all conditionals have been checked. Also, the is_page() function doesn’t allow parameters to be passed in on a bitwise basis. So simply change your code to the below and you’re good!

<?php if ( is_page('Our-Team') || is_page('Representation') ) echo "page_active"; ?>