If I understand the question correctly you need a copy of the sound files. Put them in the Notifications folder in your internal storage and then go into WhatsApp's settings and choose one as your notification tone for that app.
(Not having an iPhone I don't know what the iPhone WhatsApp tone sounds like - wouldn't have known it was different from the Android one, and am slightly surprised if they have a specific tone that it isn't cross-platform, as that would make most sense in terms of brand identity).