Yes, of course, you can bring someone for a conjoint session! I encourage (but never require) all of my clients to bring someone significant to them for one or more sessions – maybe a family member or best friend or significant other who would be willing to join you. Sometimes it is for support, sometimes it is to resolve a conflict.
Sometimes it just reveals something that otherwise may not have come up with the client alone. No person exists in a vacuum! We are social creatures who operate in an environment with other people. We can discuss this more with respect to your own personal situation, but in general others are welcome.