I mean, for the record, its as Franky said. They are a Yonko crew now. Killingham, Gunko and Sommers have country ending powers and if Luffy's group didnt exist with Loki then Elbaph would be gone.
We also dont know how these 3 are relative to Shamrock, and what he is relative to Gorosei or Shanks himself
Could these 3 alone face Yonko? Probably not. But if all 8(?) were together with Shamrock, who may or may not be relative to Shanks, then its possible.