That is so sad! Animals and birds grieve for their companions, too. With time, their grief will lessen and they will adapt to life without him, as we do.
What I try to do is provide attention, treats and activities they might enjoy, as a diversion. I know you are doing some of that already. Maybe try something irresistible, like a few mealworms. If they're normally in a run, maybe give them a pot of wheat grass. Or a little clump of sod, so they can eat the grass and dig through the dirt. Or take them for a little walk in the yard. A change of scenery and some exercise is always good.
Mostly, they just need time. I'm sorry for your loss, as well. You obviously have a very kind heart.