Android : Database for cross platform mobile apps

I'm currently creating an app, initially on Android and once completed also for IOS.

I need a database which all users will be able to access, i.e. if an Android user updates their location another user on Android or IOS will be able to view the change.

I've only ever had experience with the built in sqllite database for Android, so this is completely new to me!

I've been trying to research this for a while now, and I'm struggling to find a definitive answer. From what I understand I could get web hosting and create a resful front end which would allow me to access the database on the hosted server, and then I would be able to use the restful api in my Native mobile apps and receive data back, by the looks of things potentially in a JSON format? Is this correct?

Also on the server I will have an XMPP server running so that I can use chat functionality, would it be possible for the XMPP server to access the database as well?

Finally, if I am on the right lines, could anyone point me to potential solutions for databases/hosting or guides? And if I am not on the right lines, could someone tell me where I am going wrong!

Thanks for any help! Matt