Deni was supportive to a fault and had the priceless skill to be able to deal with Wayne, so Khan could modify the journey's arrangements without encountering any challenges.
After exhausting the talks and dealing with another general conversation, Khan sent Deni and Wayne back to the human ship, allowing them to continue following him.
That was merely due to a lack of space. Deni and Wayne were welcome additions to the crew, but Khan's ship was too small for five people.
Moreover, Liiza's meal demand increased by the day, forcing Khan to stock more and more supplies at each stop. The cargo area was often too cramped to be anywhere close to livable, and Zalpa didn't do roommates, so splitting the crew between the two ships became necessary.
Of course, privacy was another factor that played a part in that decision. Liiza was barely holding on as she was, so adding her father's constant presence to her surroundings could drive her crazy in no time.
