Ugh, I can't even... I'm 300% done with people's confusion over wielding weapons and armor spikes and stuff. Here's the breakdown again, for the umpteen billionth time.
1) When you make a full-attack, you can make your normal iterative attacks with any weapon you have ready. That means that if you have a Longsword in each hand, armor spikes, and a boulder helmet, and 3 iterative attacks, you may use any combination of these 4 weapons (5, technically, as anyone can make an unarmed strike) to deliver three total attacks at full BAB, BAB-5, and BAB-10. Repeats are OK. This is not two-weapon fighting so you suffer no attack penalties and none of your attacks are off-hand so they all get normal Str to damage. This goes for 2-h weapons as well so, in your case, you have 3 weapons ready to use; Guisarme, Armor Spikes, and Unarmed Strike so you can make a full-attack and mix-match whichever of these weapons you like so long as you stick to your normal BAB allowance.
2) You do not need to have attacked on your turn with a particular weapon to threaten with it. Even if you didn't attack at all (ie, you double-moved), you still threaten with any and all weapons you have ready. Attacking with your Guisarme, in no manner whatsoever, affects your ability to threaten with any other weapon you have available, including Armor Spikes. Furthermore, even if you did use TWF on your turn with, say, a Longsword and Armor Spikes, once your full-attack is ended, you no longer suffer TWF penalties so you could make an AoO with either weapon and no longer take the -2 attack penalty and both would deal full Str to damage.
In short, your GM is wrong.
