I am in Cairo and I have level 35 miracles and I think I should grind everyone in my party is level 20 to 30 and I was wondering what level I should grind to if anyone can help please respond.
I think you should be around level 40 ish in Cairo. That's when you get stronger skills for Miracles. Level 20 seems to be kind of low for doing the final portion of the game in my opinion.
I'm doing the character endings and it is either the Jotaro or Kakyoin ending this is my first playthrough of the game do I need to level up one or two characters more than the others?
Only FP (not the level of the characters) matters in character endings, but I recommend leveling up the character you want the ending with for the fights in the final stretch of the game.
Dio in Kakyoin's ending is technically harder because you can't fight the one where The World is a separate enemy. However, I think you get both Jotaro and Kakyoin on your team for Kakyoin's route.