Android : [Android]How to develop a small application to share images between other devices

We have a small group, and need to share our data (Images/Feed news.) Some one view data only, and some one can full control data. Group size is smaller than 100 peoples and closed group.

This application supports iOS & Android both.

I known a few solution, but it's too difficult for using & took too much time for developing.

1. I dont want develop a server data storage. Because, need an administrator.. and fee monthly


2. I dont want to use Dropbox, Because it cannot control access file.. and user cannot use 2 accounts on their device.


3. etc...

I think Google App Engine is total solution & easy for developing.. I have some unclear points, please help me explain them..

1. 
   

   If use Google Drive, Why cant share App data? (It's private data, only can access by itself)

   
   


2. 
   

   Is it ok? if i use Google Cloud Storage? Is it easy for developing?

   
   

Please recommend me a easy solution..

Thanks so much