Ring desktop & App to multiple extensions

I'm set up so that when someone calls our extension 6000 is goes to multiple people that are a mix of physical phones and app users that each have their own extensions. I can't figure out how to make it so the app users are able to receive calls when the ex 6000 is set to ring desktop & app. The only way around this is to have the apps users cell phone number entered in the call forwarding but then it won't use the app and therefore those users can't transfer calls.