Check iTunes and see if you have a pending or stalled download in there. If you do, finish that download or delete it if you can. If you can't finish or delete the download on the iPad, do it in iTunes on your computer and then sync the iPad. Then go back to the apps and see if they will download.
If that doesn't work or if that was not the problem, go to Settings>Store >Apple ID, tap your ID and sign out. Then reboot the iPad, Reboot the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons.
Then go back to Settings>Store>Sign in and sign in again and see if the apps will download or update.