Oh, I'm so sorry to hear about your grandfather's long illness and death.
I'm sure it has been hard for you to deal with. Times like this are where it's easy to revert to habits that aren't the best--and it sounds like this is what you've done.
You should feel free to talk to your parents about your feelings. They will understand, even though they are grieving, too. And you might find that your housemates understand more than you think they would, especially if you talk one-on-one.
You know that food won't fill the empty space left by your grandfather's death. So one strategy you might use is to make sure you have weight-friendly foods in your house that are just for you. I don't know how you do foods in your living situation, but you should be able to keep your own snacks, at least, so that others don't eat them. And then turn to these foods in serving-size quantities when you want to eat. At the same time, try to stay away from the junk foods that can only make things worse.
I know you know these things--I just wanted to reinforce it for you.