Williams then punched the tourist when he got out, resulting in a cut to the man's chin.
Williams demanded money and when the tourists said they did not have any, the Argentinian was punched to the head and kicked multiple times while he lay on the ground.
The Polish tourist was punched in the face twice, causing her to fall and bleed from the nose. The demand for money continued and Williams later removed groceries from the campervan.
Calls for help from the tourists were not heard but the woman managed to run to a nearby house and raise the alarm. She suffered a black eye and severe bruising to her face.
The other tourist had a fractured rib, and injuries to his back, torso, and chin. The international visitors were taken to hospital, but were discharged later the same morning.
Williams was remanded back in custody while Nathan is on bail. Both will be sentenced on April 27.
Justice Kit Toogood has called for pre-sentence reports for both men and a home detention report for Nathan prior to their sentencing.