If I have web and android app that share same data and user can sync between them, but I deicide to charge for "premium" features which can include storing pictures and other stuff which take space on the servers outside android, can I charge for those features (on subscription bases) on the web and unlock them automatically in android while subscription is running without getting banned from the play store? Also can I also use some other mobile payment processor, for example paypal to charge for that subscription directly from android app if it will unlock the features on both web and android app? This is what I have found relevant in the developer content policies :
In-app purchases: Developers offering virtual goods or currencies within a game downloaded from Google Play must use Google Play's in-app billing service as the method of payment. Developers offering additional content, services or functionality within another category of app downloaded from Google Play must use Google Play's in-app billing service as the method of payment, except: where payment is primarily for physical goods or services (e.g., buying movie tickets, or buying a publication where the price also includes a hard copy subscription); or where payment is for digital content or goods that may be consumed outside of the app itself (e.g., buying songs that can be played on other music players). Developers must not mislead users about the apps they are selling nor about any in-app services, goods, content or functionality they are selling. If your product description on Google Play refers to in-app features to which a specific or additional charge applies, your description must clearly notify users that payment is required to access those features.
In simple word if your app is the only thing you got, you must go through google payment service but if you are selling your service through multiple environments(desktop/ios/windows mobile) and Android is one of it you are ok.
Example; CBS app, where once you pay you can watch shows in desktop, Android or in iOS platform and they use third payment processors.
But, if you are selling your app through a third party payment service, it is not ok. For example, you developed a Chess game app which can be downloaded free from Play store. But after the download user have to pay and you are collecting payment using third party payment service like Paypal. This same goes for any other app features or digital contents.
In one of the place i worked where my company was selling app to end user. We have the same app for Android, Desktop and Windows mobile. When a user is paying for Android app they will not got Desktop version for free or Windows Mobile version. There were separate license agreements for each app and user have to pay for each license separately. I remember on that instance our company lawyer suggested we should distribute our app outside Play store.
But finally i will recommend you to consult a legal expert who understand digital content policies. Better safe then sorry.