Is it possible to intercept/hack a WhatsApp conversation between two people or messages sent to a group and how safe is WhatsApp call? Is eaves dropping possible in anyway?
WhatsApp has an end-to-end encryption feature, this should protect you from most threats.
Here's another thing, WhatsApp is compromised by NSA. Its mother company, Facebook, has been proven to be in NSA's PRISM program. So, if the NSA is in your threat model then I'd advise to avoid WhatsApp and use a more security-oriented OTR software, like Signal, or Wire.