GOD HAS MADE NO COVENANT WITH GENTILES

[jeremiah1five]

God has made Abraham a Father of many nations are those all his biological descendants?. God has given the right for those who received Christ and believed in His name to be called the children of God.
The Spirit himself testifies with our spirit that we are God’s children.

So the children of God are not in any covenant relationship with the one who decreed such?

I agree. But God made no covenant with Gentiles. The covenant in which Gentiles enjoy are the blessings of Abraham's covenant but not the covenant God made with the person which is a natural covenant and as we later find out is spiritual in nature too.
Gentiles enjoy the spiritual aspect of the natural covenant God made with the person Abraham and his descendants.
Abraham had two sons. One is Isaac and the other is Ishmael. Isaac also had two sons Jacob and Esau. Although Ishmael and Esau received blessings from God the covenant from which Jesus was eventually born went through Isaac. Ishmael had twelve sons like Jacob/Israel and Esau had his descendants. These descendants are the 'nations' and 'kings' that would come "from thee" (meaning Abraham.)

6 And I will make thee exceeding fruitful, and I will make nations of thee, and kings shall come out of thee. Gen. 17:6.

And you should know that Gentiles do not come from the loins of Abraham. So, these 'nations' and 'kings' that "shall come out of thee" must be identified as the descendants of Abraham through Ishmael, and descendants of Esau his great grandson. But not Gentiles. Gentiles do not come from the loins of Abraham.