"Not My People" Become "My People"

Yet the number of the children of Israel shall be like the sand of the sea, which cannot be measured or numbered. And in the place where it was said to them, "You are not my people," it shall be said to them, "Children of the living God." (Hosea 1:10 ESV)

"And in that day I will answer, declares the LORD, I will answer the heavens, and they shall answer the earth, and the earth shall answer the grain, the wine, and the oil, and they shall answer Jezreel, and I will sow her for myself in the land. And I will have mercy on No Mercy, and I will say to Not My People, 'You are my people'; and he shall say, 'You are my God.'" (Hosea 2:21-23 ESV)

As indeed he says in Hosea, "Those who were not my people I will call 'my people,' and her who was not beloved I will call 'beloved.'" (Romans 9:25 ESV)

Once you were not a people, but now you are God's people; once you had not received mercy, but now you have received mercy. (1 Peter 2:10 ESV)

Ephraim was changed from "not my people" to "my people".
Gentiles who became Christians were changed from "not my people" to "my people".

So the following could be true:

1. Gentiles who became Christians will join the tribe of Ephraim during the millennial kingdom.
2. Some Christians could be the descendants of the lost tribes of Israel and will rejoin their respective tribes during the millennial kingdom.