Total damage after accident

Good evening together, My father had an accident with our mercedes vaneo today. To the accident process: Father drove a highway at about 70kmh, suddenly a car (Dacia Logan) raced from one side of the road and took my father’s car with him. The entire passenger side was destroyed at the back, the mature including brake was thrown away about 200m. My father is doing well according to the circumstances. The tragic – our dog was in the trunk. He was dragged out of the rear window What happens now? The perpetrator drove with another person’s vehicle and we don’t know how to go on. There are, of course, several witnesses. Only – who pays now what, how long does it last? How can we stay mobile? And what does the insurance of the accident opponent carry? What can we expect from the insurance? And since we have lost our dog :'( we must cremate this morning…. Is this also paid or are we sitting on Data about the car: Mercedes vaneo Family 10/2002 92.000km down (kept) New TÜV High equipment (6 seats, seating, navi etc.) Thanks for your help already