Who "we" are is the conscious memory of ourselves. The physical body only houses that entity.
The 1st resurrection is thus described as a "seed" that is sown into an imperfect body at 1 Corinthians 15. So for the first resurrection, those who died in Christ and must be resurrected before the millennium are actually implanted into living modern anointed ones and thus they share a body and identity. The living anointed ones perhaps experience the "memory" of a previous life.
That's why the 1st resurrection is completely invisible! But that is also quite brilliant to resurrect the past dead into the bodies of the modern living because there are no adjustment or orientation issues. Those resurrected come back speaking a modern language and having all the knowledge and history of what happened from the time they were first here until now!
At the second resurrection, obviously individual bodies will be provided for the dead who come back much like the "angels" and thus in bodies that are likely androgynous, that is, having both aspects of male and female. There will be no marriage at this time and no new children; but that doesn't mean there will be no sex. Only, since everyone is unisexual at this point, it will be possible to have an intimate (sexual) relationship with every other human on the planet, sort of like in a big, open marriage. Now imagine if there were say 4 billion people on the planet who end up getting everlasting life. Let's say a computer program arranges for you to meet and live with each person on the planet for a year in a different location on the planet every other year. This process would take 8 billion years to complete. That is, at the end of 8 billion years, you will have lived with and had sex with every other human on the planet and likely lived in every single city, apartment and home on the entire planet as well! God's greatest creation in the earth are humans!