Paul, an isrealite by birth, was aware that the promise was made to the 'house of Isreal' and he spoke to gentile christians about this in Romans chpt 9.
However, in Romans 9:6,7,8 he stresses the fact that "not all who spring from Isreal are trully Isreal" but the 'seed' are the 'children of the promise'
He clarifies who the 'children of the promise' are in Galatians 4:28 He was speaking to Gentile christians for in Gal 5:2 he discusses cirmucision and says "if YOU become circumcised, Christ will be of no benefit to YOU" So he wasnt speaking to Jews here but rather uncircumcised believers.
Now, if you want to hold to the belief that the 'house of Isreal' only applies to a natural born Jews you are welcome to do that, but I will stick to the bible in this regard and to the writings of Paul who was inspired by holy spirit to write:
Galatians 3:29 "Moreover, if YOU belong to Christ, YOU are really Abraham’s seed, heirs with reference to a promise."
Paul is speaking these things in a figure, not a physical reality. Isaac was truly born of promise, of faith, not of flesh. Such is what makes us heirs. However, to dismiss the truths and the prophetic utterances pertaining to the fleshly promises given to Israel, and their fulfillment to come is to deny the word of God, and to make His words fit our beliefs instead of the other way around. This is a common practice in those who do not understand how to correctly divide the word of truth. It is for the purpose of supporting theology instead of upholding the truth of the Scriptures. It will certainly aid in retaining opinion, but such opinions result in the denial of God's declarations.
fivesense