One great thing about the prodigal son parable is that it can be interpreted a number of valid ways.
But I don’t know why the older son would represent the people of the first resurrection, since presumably they’d know better than to complain about the salvation of the younger son. (Also there’s no first-resurrection parallel for them in the parable.) Maybe they represent the survivors into the millennium, or those born during that time, who come to think their status as ‘never having fallen’ must be useless if God is willing to save people after the general resurrection (still to come in their future), and so their underlying resentment at serving God becomes exposed.
That would fit well with the oddity of Satan managing the greatest final rebellion after the passing of the millennium reign; but then they wouldn’t really be the older brother, since the great majority of people not yet saved from hades were there first. 
We’re probably overthinking the parable trying to make it work out in that much detail.
If it serves (among other things) to warn Christians not to resent the salvation of punished sinners out of death and destruction (as the father describes the younger son’s condition), that’s good enough and allows a wider scope of application in principle. 
Bodily resurrection is one sign of God’s commitment to restoration, instead of just trashing people (and Nature). I gather from testimony like 1 Peter’s that people can be saved out of hades directly by God even before the first resurrection; but those who refuse to repent must stay until the general resurrection. If they still refuse to repent, Gehenna continues until they learn to reject their sins, but they continue in their bodily life which is itself a testimony of God’s continuing commitment to saving them.
So in that day, the impenitent can see what repentance brings (bodily “eonian” life, not merely ongoing bodily life), and they also have immediate evidence that God intends the same for them and isn’t only being spiteful (because they have in fact been bodily resurrected, too).
I expect the body helps lead them to repentance in its own way and teaches them through its own ways of suffering: before the resurrection they suffer for fondling their sins, after the resurrection they continue that but add bodily suffering back, as further inescapable evidence that they should stop fondling their sins.
What would be pointless would be to resurrect them hopelessly to ongoing life, and even more pointless (if that was possible) to resurrect them only to annihilate them out of existence!