iPad apps randomly going gray screen or Home
The iPad 2 is an old device. This lends itself to many crashes. 

What you are describing are app crashes. It happens on all devices, but much more frequently on older devices. Since the apps have been updated for never iOS versions, like iOS 10, the iPad is not technically supported by the apps that you're trying to use. 

Also, having some extra storage space never hurts, so try deleting some apps to clear up some space.

Beyond deleting apps, the only advice I can give you here is to upgrade to a newer device. Your device is 6 years old, which is a long time for mobile devices.