A 4-day trip entirely within Volcanoes National Park gives both primate treks without needing Lake Kivu or Nyungwe.
Day 1: Kigali to Musanze
The drive to Musanze.
Day 2: Gorilla Trekking
The core trek.
Day 3: Golden Monkey Trekking
The shorter, lower-altitude trek.
Day 4: Return to Kigali
The transfer back.