I have a cellular apple watch connected to my fathers iphone. Can I make and receive calls when the iphone is not around and which cintacts will be shown on the watch

Definitely! Cellular Apple Watch models doesn't require the paired iPhone to be around it. You can make and receive phone calls even if it's far away or turned off.

Additionally, all the contacts on your iPhone will be synced and shown in your Apple Watch.

So, you have direct access to make and receive phone calls and even text messages to all the contacts.

However, in order for your cellular Apple Watch to work in such manner, make sure that cellular connectivity is set up on you watch with a supported carrier.

Whatever contacts are on the phone will also be on the watch.