Because of the Trinity, they have all three always existed as one. Only God knows how God works, tho. Our minds can't comprehend it.
Discussion
And you can't really say what is first, when They existed before time existed. Outside of time.
so do we, technically speaking, it's only our story that is time bound
So this is going to be a sophism, but we don't want to make the debate boring. If only God knows God and you can't comprehend God, how can you be sure about anything? How can you be sure that Bible is telling the true? What if it is yet another golden calf? What if it is yet another test if you would follow the book or your heart? How can you use something you don't understand and you can never understand in an argument?
You cannot be sure. You take it on Faith, out of Love and that gives you Hope, but the greatest of these three things is Love.