I did a lot of research and apparently its impossible because if different database formats the messages are saved on two platforms. At least that's what I understood on some random forum.
It is possible to do so, using third party applications. I've done it with the help of a friend, although it required using paid Windows apps that looked like there was no way they could possibly be legitimate and not a scam - they worked like a charm. the process involved an application downgrade, forcing the iPhone to make local backup instead of backing up to the cloud and a handful other things, all of which where automated.
Is there something in the existing WhatsApp cloud backup feature that prevents you from bringing those backups between iPhone and Android?