Read Hebrews. You can't have two covenants.
I don't know why you say that. Most scholars I have heard about recognize seven separate covenants. Since they are established with different groups they are all in force at the same time.
I'm not sure I can name them all. There's the Adamic, Noahic, Abrahamic, Mosaic, Davidic, and Christian. I'm missing one.
But that doesn't have anything to do with what we owe the Jews. Look at Romans 11-13. Paul lays it out that we owe them a debt of gratitude.