Why am I unable to download a family shared app?

We have 2 ipads in my home and have the family sharing program.

I have unsuccessfully tried to download a shared app for my Grandchildren. I am the adult responsible for paying for apps etc.

When I try to download the app on my Husband's ipad. It loads, then when I press on it I get this message," This app is no longer shared with you. To use it, you must buy it from the App Store."

I then click on "View in App Store"

I am sent to the app store and the app I want. I click to buy it and it looks like it is downloading.

When finished, I click on the app to open it and the whole thing starts over again.

The messge " This app is no longer shared with you........yada yada yada!!! The operating system is IOS 9.0.2

I have the App working on my ipad and it opens perfectly.

What is the problem??