Scripture for OT saints being included in the first resurrection
Hebrews 11:39-40 - Old Testament saints perfected with the church.
39 And these all, having obtained a good report through faith, received not the promise:
40 God having provided some better thing for us, that they without us should not be made perfect.
Matthew 8:11-12 - Abraham, Isaac, Jacob in the kingdom.
11 And I say unto you, That many shall come from the east and west, and shall sit down with Abraham, and Isaac, and Jacob, in the kingdom of heaven.
12 But the children of the kingdom shall be cast out into outer darkness: there shall be weeping and gnashing of teeth.
Luke 13:28 - Old Testament saints in the kingdom.
28 There shall be weeping and gnashing of teeth, when ye shall see Abraham, and Isaac, and Jacob, and all the prophets, in the kingdom of God, and you yourselves thrust out.
Ephesians 2:19-22 - Church built on Old Testament foundations.
19 Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God;
20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
21 In whom all the building fitly framed together groweth unto an holy temple in the Lord:
22 In whom ye also are builded together for an habitation of God through the Spirit.
The OT saints are in the kingdom at the 1st resurrection.
The last resurrection would then Include those who become part of the kingdom from nations who obeyed the gospel during the millennial reign.