Preheat oven to 325 degrees F (165 degrees C). Butter two 8x4-inch loaf pans.
Whisk whole wheat flour, flaxseed meal, wheat germ, baking soda, cinnamon, and salt together in a large bowl. Stir walnuts into dry ingredients.
Beat eggs and brown sugar in a separate bowl with an electric mixer until thick and pale, about 3 minutes. Add sunflower seed oil, walnut oil, and yogurt; beat to combine. Stir in mashed bananas and vanilla extract.
Pour egg mixture over dry ingredients and mix briefly, until just moistened. Divide batter between loaf pans.
Bake loaves in the preheated oven until a toothpick inserted into the centers comes out clean, about 1 hour and 15 minutes. Remove pans from the oven and let sit 5 minutes, then remove loaves to cool on wire racks.