Giants are very big version of regular villager and it seems that they are neutral regarding to anyone.
There is a chance to spawn guards in village, but even if they don't, you can transform any villager into such guard, by tapping on them using iron helmet in your hand.
How to install addons:
- Download ES File Explorer
- Using ES File Explorer go to the Downloads folder on your device
- Find .mcpack or .mcworld files that you download earlier
- Click it to import into Minecraft Pocket Edition
- Open the game
- Create a new world or edit an existing world
- Scroll down into Add-ons section and select the ones you want to apply