Well, they might have a deep conversation about their different views on the world. Eren could try to convince Zeke of his more radical approach to saving the Eldians, while Zeke might push back with his own ideas of euthanasia for the Eldians. It could be a very tense encounter.
They could start to plan a strategy to deal with the Marleyans together. Since both have their own experiences with Marley, they might come up with a complex plan involving Titan powers and political manipulation. For example, using Zeke's position as a Marleyan weapon and Eren's influence within Paradis.
It might be. Since both Naruto and Attack on Titan have huge fan bases, a fanfiction like this can attract a lot of attention. The idea of Naruto, with his unique abilities, stepping into the world of Attack on Titan to save Eren's mom is full of potential for creative and exciting storylines. For example, Naruto could use his shadow clone jutsu to deal with the Titans while trying to reach Eren's mom in time.
Maybe Naruto somehow gets transported to the Attack on Titan world. He quickly realizes the danger that Eren's mom is in. Using his ninja skills, he battles the Titans and manages to rescue her just in time. After that, he might try to find a way back to his own world while also getting involved in the local affairs of the Attack on Titan world.