So this is a bit of semantics questions but the swashbuckler ability Precise Strike says that you cannot use it if you have a weapon or shield in your other hand not off hand. So could I TWF with armor spikes and a standard weapon and still use the ability.
Hands are not hands. Hands are a magical force imposing game balance on innocent PCs.
Armor Spikes: Can I use two-weapon fighting to make an "off-hand" attack with my armor spikes in the same round I use a two-handed weapon?
No.
Likewise, you couldn't use an armored gauntlet to do so, as you are using both of your hands to wield your two-handed weapon, therefore your off-hand is unavailable to make any attacks.
This is only explicitly the case for 'off' hands. What 'other' hands are is up to the GM, but it looks to me like this would be against RAI. The game wants you to be able to use two-weapon fighting OR two-handed weapons OR Precise strike, but not two of these at the same time.