> Isaiah 17
Let's not lose sight of the forest by cherry-picking one tree. The text is about a new order of things in the eschaton. Political structures will be transcended, there will be newness and re-creation, divine promises will be ultimately fulfilled, and there will be blessing and peace.
In the new creation, the agonies, pain, suffering, and even death itself will be no more (same idea in Rev. 21.4). It is not to say that nothing will be remembered. 1 Corinthians 15 tells us about the spiritual body in the resurrection of the dead which will be "new," based on the resurrected body of Christ, but remember that when Jesus came back from the dead, he knew his friends and his friends knew him. The point is re-creation, not amnesia. The new order will be so sublime that there will no longing for our previous lives. We'll move forward with wholeness, not look backward with regret.
> Matthew 25
Yes, v. 31 is about separating the saved from the damned. But Matthew 25, as well as other parables of Jesus, show a vision of heaven as being a community of people, and that was my point. You're right that we can't simply infer from that verse that it means we will know all our friends. But if we take all of Jesus's teaching under wing, we can see where his descriptions of heaven are community-oriented, such as John 14.1-4.
> Elijah and Moses
Yes, they were significant figures with an elevated status, but in pre-photography days, how did the disciples know who they were, unless, of course, they were wearing name tags.

My only speculation was that it's a small indicator that we will know each other in heaven, which addresses your question about meeting friends. From it we may be able to infer that we will also know our friends in heaven.