ANSWER: Let’s answer your first question first. The person or entity that Christ will marry is the church of God, which is composed of truly repentant and faithful believers. He marries the church in Revelation the 19th chapter. As the true bridegroom, He not only has prepared himself for the marriage but has also cleansed and prepared the bride for the glorious wedding (Ephesians 5). When He marries there will be great rejoicing in heaven! For example, Revelation 19 reports rejoicing in heaven when God’s kingdom takes control of the world and the wedding of the saints is revealed.
'Praise God! For the Lord, our Almighty God, is King! . . . For the time has come for the wedding of the Lamb, and his bride has prepared herself for it. (Revelation 19:6 - 7)
Hence, it should be no surprise that the guests at the wedding supper are righteous Christians who praise and bless God, and call attention to the blessing of being part of the Lamb's marriage supper (Revelation 19:9).
Those who wish to be saved respond to the command, "Come," just like the Bride does, in Revelation 22:17. Notice also that the great city of God, the New Jerusalem, where Christians will live forever with God the Father and God the Son, is called the bride of Christ in Revelation 21:9 - 10. Paul in Ephesians makes an analogy between a man married to a woman and Christ and the church (Ephesians 5:23, 31 - 32).
Now let’s answer your second question in more detail. Look carefully the parable that’s part of the Olivet Prophecy in Matthew 25. The ten maidens or virgins had to wait for the bridegroom to come. Symbolically, they represent the church while the groom is Jesus. When He comes, five of the maidens who were so apathetic spiritually missed out on marrying the bridegroom, who is Jesus (verse 10). Those Christians who were ready went into the marriage feast while the others were shut out.
Finally, consider reading the parable in Matthew 22:1 - 14. Note that the bad servants, who represent people who rejected Jesus as Savior, choose not to go to the wedding feast. Then one man chooses to go, but he does not spiritually clean himself up, which is symbolized by his not wearing the right clothes for a wedding, so he’s thrown out. So it’s obvious that the (proper) wedding guests are called and faithful believers in God.
So I hope that these answers have been helpful to you. The church is the bride of Christ while the wedding guests are faithful Christians.