What can my sisters and I do to help my dad heal from the loss of my mom?

I am very sorry to her about your mother ping. Being there with your dad as much as you possibly can right now because of the sudden shock of your mom ping because whenever yall are not there it hits him that he is now alone. Being active is the best thing you can do. You guys need to get out of the house and maybe go on a long walk together through a park or going on a hike. He needs yalls support, I am sure after a couple weeks he will soon accept that fact that your mother has ped and start to make improvements. Comfort and love your father is all you can do. Tell him you love him.