Matt 13:43 Then the righteous will shine forth like the sun in the kingdom of their Father...
Matt 25:31 But when the Son of Man comes in His glory and all the angels with Him, at that time He will sit on the throne of His glory.

The millennial Kingdom will have a heavenly part and an earthly part.

The heavenly part will be the kingdom of the Father, where overcomers will reign with Christ as co-kings.

The earthly part of the millennial kingdom will be the kingdom of the Son of Man, the kingdom of the Messiah, the tabernacle of David.

There will be three groups of people in the millennial kingdom. The first are the overcoming saints, including the overcoming saints of both the Old Testament and the New Testament. These overcoming saints will be co-kings of Christ.  Christ is the highest King, and we shall be His sub-kings. This is the upper portion, the royal potion of the millennium.

The second group, is the preserved and proper Jews, who will be saved at the time of the Lord's coming back. According to Zechariah 12:10-14, these Jews will look on Him whom they have pierced, and then they will repent. These are the ones who will pass through fire and be refined in Zech. 13:9. These saved Jews will enter into the millennial Kingdom as priests and will teach the nations to seek God and to know Him. This is the lower portion of the millennial kingdom.

The third group of people in the millennial Kingdom will be the "sheep" of Matthew 25.  These "sheep" will be transferred into the millennial kingdom to become the citizens there. These saints are also in the lower portion of the millennial kingdom.

Exerpts from HWMR- Minor Prophets, Volume Two, Week 7-Day 4