Extra Class Grands!

Question about Extra Class Grands! So I'm currently prepping for my future Grand Servants and have seen that we get two Extra class Grands. Do we have to choose one Extra 1 Grand and one Extra 2 Grand? Or can we mix and match? For example, can I choose Two Rulers for my Grand Servants? Or can I only choose one ruler and one Extra 2 servant? My plan is to Grand OG Jeanne Ruler and Avenger Jalter, but I know they're both Extra class 1 so I don't know if I'll be able to. Any help would be appreciated! Thanks in advance!