Read Revelation 20:4-5 carefully. A group is resurrected before the millennial kingdom and a group is resurrected after the millennial kingdom. Both resurrections are referred to as the first resurrection so that means the first resurrection is split into two groups.
No, the second resurrection is not part of the first resurrection. Man created the chapters and verses and punctuation. The passage should be understood like this:
But the rest of the dead lived not again until the thousand years were finished.
This is the first resurrection: Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.
"But the rest of the dead lived not again until the thousand years were finished" is the second resurrection that happens at the GWTJ when people come from hell and death etc.
This interpretation, which i believe is actually accurate, doesn’t contradict any other verses or cause any issues as far as I can see.
Those of first resurrection cannot be hurt by the second death. If you erase the second resurrection and make it part of the first resurrection then no one can die the second death. That's a contradiction.
Gill:
This is the first resurrection;
which is not to be connected with the living again of the rest of the dead at the end of the thousand years, for that will be the second and last resurrection; but with the witnesses of Jesus, and the true worshippers of God living again, in order to reign with Christ a thousand years; for this resurrection is not meant of a resurrection from the death of sin to a life of grace; though the work of grace and conversion is sometimes so represented, it cannot be designed here; for such a resurrection the above witnesses and worshippers were partakers of before their sufferings, and which was antecedently necessary to their witness and worship