Went up against a glowing one and it seemed downed ghouls rose up again? Are these ghouls truly undead?

Sort of, as long as the ghoul hasn't be dismembered in some way, the Glowing One's radiation pulse will bring them back, though with only a fraction of their health.

Reanimation through radiation.

Makes battles tough, when you're still trying to get through to the glowing one and he keeps bringing them back. Worse, when there's two of them and they keep bringing each other back

As soon as I see there is a Glowing One I focus all my energy on it. I completely ignore everything else going on and will go out of my way to destroy the Glowing One first. I've had to spam stimpaks and rad away just to kill a Glowing One.

Kind of makes sense considering that there isn't that much to be restored anyway and that radiation heals them. A body isn't 100% when someone dies. Many cells are still active a long time after a human has died. Ghouls are a lot more resiliant than humans in terms of their life spark. They even age slower.

Ghouls are mutant humans, they aren't undead. Glowing ones are super irradiated ghouls, radiation heals them.

Right but the ghouls were killed by me(they werent stunned) therefore they are now zombified

It's a miracle. PRAISE ATOM!

Molotov cocktails, anyone? Massive area, decent damage, lingering damage, non-radiation damage...

Just aim at their legs in V.A.T.S. They go down pretty easily. Once down, you can concentrate on the other ghouls, which probably swarm you in the meantime and finsih the job with a few headshots afterwards.