The verses you quoted support my contention that Spiritual Israel is comprised of those "descended from Israel." Did you miss that or something? Paul is talking about his brethren, his kinsmen. (verse 2) who lean on the descent from Abraham with regard to the promise God made to Abraham and his descendants. In that context, he tells you, "It is through Isaac that your offspring will be reckoned." Again, a reference to a child born from Abraham's own body. (Genesis 15:4) The Jews are not incorrect with regard to physical descent. Paul makes this very point at the beginning of his argument.
Romans 9:1-5
I am telling the truth in Christ, I am not lying, my conscience testifies with me in the Holy Spirit, that I have great sorrow and unceasing grief in my heart. For I could wish that I myself were accursed, separated from Christ for the sake of my brethren, my kinsmen according to the flesh, who are Israelites, to whom belongs the adoption as sons, and the glory and the covenants and the giving of the Law and the temple service and the promises, whose are the fathers, and from whom is the Christ according to the flesh, who is over all, God blessed forever. Amen.
We see from the above passage that the promise belongs to Paul's brethren, his kinsmen of the flesh. The adoption of sons belongs to
them. Every item in Paul's list above belongs to his kinsmen. We won't understand what Paul says from here to chapter 12 unless we anchor our minds with the first five verses of chapter 9.
Paul is not suggesting that Physical descent is irrelevant. Bear in mind that he is talking about a subdivision of those born of Israel, i.e. Jacob. Among those born to Jacob, there exists a subgroup of people who are the children of promise.
Paul is making a different point here in Galatians 3, than he made in Romans 9. Here the question is centered on God's promise to Abraham with regard to his blessing. Gentiles are included in that promise because God promised Abraham, "In you, all the families of the earth will be blessed.” And the question here is, "Who are Abraham's seed?" We are all children through faith. Romans 4.
Paul addresses God's promise to Jacob in Romans 9. This chapter answers to the question, "who is a child of Israel with respect to God's promise to Israel. Galatians 3 is talking about a promise God made to Abraham; Romans 9 is talking about a promise God made to Israel (Jacob.) Thus, Paul can argue that descent from Abraham is not the sole criterion with respect to the promise made to Jacob.
Granted, all those who have the faith of Abraham, whether Jew or Gentile are sons of Abraham and stand to inherit the blessing of Abraham. Abraham is the father of all those who believe. Romans 4:9-12 And according to Genesis 12, the blessing applies to all of the families of the earth.
Nonetheless, In his epistle to the Galatians, the Apostle places all believers in Christ; By contrast, in his epistle to the Romans, the Apostle recognizes a subgroup of Israel's children to be the children of promise. These are two different subjects. Why? God not only made a promise to Abraham; he also made a promise to Jacob.
When is the time? Let's review. The middle section of Paul's epistle to the Romans is structured as a series of rhetorical questions. For instance, beginning in Romans 6, he asks, "What shall we say then? Are we to continue in sin so that grace may increase?" Here in chapter 9, the argument progresses to the next question, which is implied, "What are we saying then, Did the word of God fail?"
This presents a question to Bible students. What particular word, what particular promise is in view here? In the first five verses, Paul indicates that "the adoption of sons" belongs to his kinsmen of the flesh. But that is only part of the answer. The rest of the answer is found at the end of his argument.
Romans 11:26-27
and so all Israel will be saved; just as it is written, “The Deliverer will come from Zion, He will remove ungodliness from Jacob. This is My covenant with them; When I take away their sins.”
The promise above is yet to happen. That particular promise God made to Israel is the promise Paul has in mind when he says, "It isn't as if the word of God has failed." And here, in this context, removing ungodliness from Jacob involves much more than forgiving the sins of Jacob's descendants. Removing ungodliness from Jacob involves destroying the ungodly.
You and I disagree on the overall narrative in Romans 9-11, mainly because we disagree on the question Paul intends to address.
