In the new testament we read that Christians are accounted as Abrahams seed through faith. When you allow the "seed" to be as it was meant to be read ... ie: all his descendants ... including those by faith ... who are the wild grafted into the true ... then you can find the fulfillment of those prophesies.
And when at the end of the 1000 years ... at the great day of Judgement ... when ALL the rightious shall stand in one place ... they shall be "the great multitude" of Rev 19.
The righteous shall inherit the new earth which has been redeemed by the death of Jesus on the Cross ... and this will be the fulfillment of the promise to Abraham.