.South America - First Trip to the Continent

I need advice from experienced travelers with knowledge of budget travel to South America. We are a family of four (spouse and two adult children).

We need help planning a 15-day itinerary.

We are considering starting in Argentina
Day 1 & 2 - Buenos Aires
Day 3, 4 and 5 - Iguazu (ideally, we would like to experience it from both sides, including Brazil)
Day 6, 7 and 8 - Cusco
Day 9 and 10 - Machu Picchu
Day 11 and 12 - Lima
Day 13 - End of trip and return