Typically when it comes to security you want to grant the least privileges that the user needs to do its work. If these 5 users are only doing read, write, and execute type of actions, then DB_OWNER seems excessive. If the databases have schemas then a handy trick is to use permissions at the schema level instead of each individual object, for example:

GRANT SELECT ON SCHEMA::[schemaname] TO

GRANT INSERT ON SCHEMA::[schemaname] TO

GRANT UPDATE ON SCHEMA::[schemaname] TO

GRANT DELETE ON SCHEMA::[schemaname] TO

GRANT EXECUTE ON SCHEMA::[schemaname] TO

http://msdn.microsoft.com/en-us/library/ms187940(v=sql.105).aspx