Well, perhaps in the 'rwby meets god fanfic', the god has come to Remnant (the RWBY world) because there is some sort of imbalance or threat that only the RWBY team can help with. So the god decides to guide them, and along the way, the RWBY characters learn about the true nature of their world and their destinies. They might have to make some difficult choices as the god presents them with different paths.
In a 'rwby meets god fanfic', Ruby, Weiss, Blake and Yang are the most likely main characters as they are the focus of the RWBY franchise. But depending on the direction of the fanfic, other characters like Penny or Jaune could also be important. Maybe Penny has some connection to the god due to her robotic nature, or Jaune could be the one who accidentally stumbles upon the god's arrival and then informs the RWBY team. Still, the RWBY girls will probably be the ones with the most significant interactions with the god.
Well, 'monkey god rwby fanfic' could potentially be a fanfic that combines the RWBY world with some sort of monkey god mythology. It could be about how this monkey god interacts with the RWBY characters, perhaps helping or hindering them in their battles against the Grimm. It might also explore the cultural and power differences that this god - like being brings into the RWBY world.
The god brothers themselves are likely to be main characters. Since it's a 'rwby god brothers fanfic', they would play a central role in the story. Also, the main characters from RWBY, like Ruby, Weiss, Blake, and Yang, might also be main characters as they interact with the god brothers.
One common theme is power. Since it involves a god, the idea of the power that comes with a connection to the Faunus god is often explored. Another theme is identity. Characters may struggle with their identity as Faunus when they are linked to the god. For example, they might question their place in the world or their relationships with other Faunus.
One idea could be that the RWBY characters are transported into the Overwatch universe and have to team up with the Overwatch heroes to fight a new common enemy, like a powerful omnic - Grimm hybrid. Another could be a friendly competition between the two groups in a series of combat trials to see who is more skilled.
One idea could be that Goku accidentally travels to the RWBY universe during a sparring session that goes wrong with Whis. He could be mistaken for a powerful Grimm at first, causing chaos. Then, he teams up with Team RWBY to fight a new super - strong Grimm that threatens all of Remnant.
Nora could also be a likely candidate. She's very energetic and not one to be intimidated easily. When she sees Goku's amazing power, she would probably be excited and want to team up with him right away. She would be constantly asking Goku about his world and his powers, and they would bond over their love for combat and having a good time.
Well, Ruby might be super excited at first. She loves new things and adventures, so seeing a Terminator could be like a new 'toy' to her, until she realizes how dangerous it is. Then she'd get serious and start thinking of ways to stop it.
You can try looking on fanfic websites like Archive of Our Own (AO3) or FanFiction.net. These platforms often have a large collection of RWBY - related fanfics, and you might be able to find the 'monkey god rwby fanfic' among them.