While iOS 8 and Family Sharing offer a lot of flexibility when it comes to sharing purchases, it seems to be causing some errors in terms of updating and downloading free apps for some people. These apps all seem to have one thing in common: they aren't Family Sharing compatible. However, since they're free, the issue can be quite irritating and shouldn't be happening at all. Luckily, there's a workaround you can try in order to bypass the issue, at least until Apple can come up with a permanent fix.
How to fix app download and update errors with Family Sharing
If you're having issues with a particular update, completely delete the app in question from your iPhone or iPad. If you can't download the free app at all, there's nothing to delete so just continue on.
Now sign out of your iTunes & App Store account. You don't have to sign out of iCloud, just your iTunes account. If you aren't sure how to do that, you can follow our guide:
Once you've signed out, don't sign back in. Follow these steps instead:
Launch the App Store app on your iPhone or iPad.
Find the app that you're having issues with by searching for it.
Tap on Get or the cloud icon, whichever appears.
Tap on Use Existing Apple ID.
You'll be prompted to sign into your iTunes account, go ahead and sign back in.
The download should now start as normal and not produce an error message.
While this is more of a temporary workaround rather than a permanent fix, it will at least get you the update or allow you to download the app in question. The problem appears to be that some app developers aren't including their free apps as Family Sharing compatible. So even though they're free, if someone else has already downloaded it, wires are getting crossed and causing issues for other family members that want to download or update the same app, even if they already had it. Just remember that this fix only works for free apps. If an app is paid and not eligible for Family Sharing, you can't download it even if someone else in your family group has already purchased it. You'd still have to buy it.
So until Apple can come up with a permanent fix for free apps on Family Sharing, give this method a try and let me know if it works for you!