How to typecast RemoteWebDriver to AppiumDriver for Web as well as native automation in selenium 3.4?

I am working on a framework based on selenium.
We are creating and executing script of
Web , Android Web and Hybrid App using selenium Grid

For Web , we are using the RemoteWebDriver to initialise the webDriver for all the browsers(Firefox,Chrome,IE) For which the code is : –

WebDriver driver = new RemoteWebDriver(sURL, cap);

For Android Web and Hybrid App we are using AndroidDirver to initialise the AppiumDriver

AppiumDriver driver = new AndroidDriver(sURL, oCap);

Now to perform different validations for Windows Web , we are using WebDriver and to perform validations on Andorid web and Hybrid , We are using Appium Driver.

Now ,typecasting Android Driver to WebDriver is working fine. But when trying to typecast RemoteWebDriver to AppiumDriver it is throwing error :
org.openqa.selenium.remote.RemoteWebDriver cannot be cast to io.appium.java_client.AppiumDriver

I want to now use only one Driver preferably Appium driver to run the scripts on both Platforms(Windows and Android).
So how can I typecast RemoteWebDriver to AppiumDriver?