1. As to Abraham's seed. - Galatians 3:16-29 adequately deals with that subject. Jesus Christ is the promised seed. Those who have faith and belong to Him are Abraham's seed and heirs according to the promise. (and note that there is no distinction between Jew or Greek in the church)
2. As to the land - Joshua 21:43-45 tells us that the promised was fulfilled in every detail. Now, if Israel forfeits their right to the land through disobedience, that's another story. But Scripture is clear that the land promise was fulfilled. Hence, no need to be fulfilled again and again.
3. As to the blessing that the whole earth would be blessed through his family - The whole New Testament deals with the fulfillment of this promise. Remember the Lord's admonition to his disciples to go into the whole earth with the gospel. Remember Paul's words in Colossians 1:6 (whether hyperbole or not) that all over the world the gospel was producing fruit. The preaching of the gospel brings God's elect into His church - His body - His bride. Wow, that was an easy one.
4. As to applying to the church and not natural Israel - One simple word: Yes!!
-ksen