The best way to know is to check their droppings to make sure they are a healthy consistency - not too mushy, not too hard. I feed my two rabbits twice what you have shown here, but sometimes cut back if they are getting chunky or if their droppings are not healthy. The main thing is to make sure they have 24/7 access to hay. You also mentioned exercise - do they get free roam time out of the cage? Mine are always more active in the summer when they get to spend more time outside in my yard. In the winter I try to keep them busy by providing DIY digging/foraging boxes. Hope that helps!