Yes, you can diagram these journeys in many different ways, and I have done this in the past although often the diagram becomes quite complex and the story gets lost sometimes.
There are a number of different approaches that I use, some of which might apply to your scenario/situation:
- Code the steps/stages in the journey in different colours for different users, to emphasise the difference in the number of steps or types of steps between different users visually.
- Create multiple lanes in the journey, one for each user, to emphasise the difference in the length of the journey or the relative complexity of each journey
- Create a journey for the primary actor/user along one axis, and then place secondary actor(s)/user(s) along the alternate axis for interactions with the primary actor/user
And you can probably combine them in different ways or formats if you need additional interactions or complexities for your journeys.