Min. requirements for Great Mothers and Morgan to be viable in GAC?

I want my new Nightsister 3v3 team to be a threat and credible on defense in GAC. Naturally I am using GM, Morgan and Nightsister Spirit. I am in Aurodium 4 in GAC, and the average opponent has at least 4 GLs. So its safe to assume in my bracket everyone has high relic characters. What are the minimum gear levels, stars, and # of Zetas needed in order for this back row defense team to be viable? I am not ready to take them all to 7star as I am working on other teams. However,  I do want this team to be hard to beat. They currently have no zetas, what zetas are needed in order to ensure they are good? And what's the zeta order of priority? Currently: Morgan G9 3 stars, Great Mothers G9 3 stars, Nightsister Spirit Relic 2, 7 stars