<?php
if ( get_field( 'other_information_check' ) && get_field( 'products_specs_check' )): // both checked
echo "4-tabs";
elseif ( get_field( 'products_specs_check' ) || get_field( 'other_information_check' ) ): // one or the other is checked, but not both
echo "3-tabs";
else: // no fields checked
echo "2-tabs";
endif;
?>