Chrono Trigger problem

I'm stuck, big time. I'm using a party of Ayla and Marle, and I'm in the End of Time right now, plus that the Black Omen has appeared. However, I can't seem to change my party. All of the remaining characters stockpiled in End of Time are rambling about various quests (such as Lucca telling me about the sun stone), but apparently none of them wants to join my party.

Is there another way for me to change my party?