These "fixes" have worked for other users when I have suggested them, but I saw a very similar post to this one a day or so ago and none of them worked for that user. However, nothing ventured, nothing gained ......
Sign out of your account, restart the iPad and then sign in again.
Settings>Store>Apple ID. Tap your ID and sign out. Restart the iPad by holding down on the sleep button until the red slider appears and then slide to shut off. To power up hold the sleep button until the Apple logo appears and let go of the button.
Go back to Settings>Store>Sign in and then try to download again
You can try resetting all settings. Settings>General>Reset>Reset All Settings. You will have to enter all of your app preferences and device settings again.
You can finish the downloads in iTunes on your computer - launch iTunes and got to Store>Check for available downloads - finish the downloads in iTunes and then sync the iPad.