Huawei has built in App Lock features you can give that a try aswell , as that won't utilize much of your extra memory.
Huawei Mate 8 builtin App Lock :
Step 1: Go to All Apps
Step 2: Phone Manager
Step 3: "App Lock"
Step 4: Setup a Password if you are using it for the first time.
Step 5: Go to "App Lock" Section and find the app which you want to lock, turn ON Lock on that App.
Step 6: Whenever you will open your Locked App it will show a password screen .
Huawei Mate 8 Applock Apps :
As shared App Locker is indeed one of the best app lock available . with custom error messages and all its the perfect solution: Install AppLock App
After AppLock i would like to suggest Privacy Knight , another App with great features . Install Privacy Knight