rear popouts are leaking

One hinge on both sides seems to be gone so it's only held in by one side each and at speed, the glass shifts and lets water in... so..... how do I fix that?

Silicone them shut if you don't really use them. I did that to a truck that had the hinges broken. I did not care if they opened.

I don't really use them, but I would like to use them as I kinda like using the rear seats

If the hinge is just separated from the glass remove the roll pin from the latch and open the window all the way use some 5-min epoxy to glue the hinge back to the window. Use a strip of cardboard on the outside glass and on the hinge and clamp with vice grips or small c-clamp till it dries then scrape any cardboard off the hinge that may have stuck during the bonding.

If the hinge is broken in the middle get a new one from the junk yard, heat the glass with a propane torch and the glue bond will break. Don't over heat it and you shouldn't get a broken window/glass shrapnel.

am I leaving the two hinges attached to the car when I'm doing this?

If you can remove the window and hinges fromhe car it would probably be easier. But it can be glued while in the car.

I don't know if I've got a clamp big enough to go through the D-pillar and hit the hinges

^^^^remove roll pin and open window all the way
this allows the window to open up enough to clamp from the bottom of the vent window.

*smacks head*
durrrrrrrrrrrrrrrrrrr

If that fails PM me, I have a few spare windows with good hinges.

thanks