Really isn't helping lol. If he has no work, he's probably considered looking for a job already, or is in the process of doing so.
Im gonna take a wild guess and say you actually can't spend sometime with grandma anymore? If you're able to, even if it's not *staying* with her during the time they are overseas, it's always nice to visit (I used to be in the same situation when I was younger) but I still visit my nan when I can, cause she cooks nice stuff and it's always nice to see her, as she tells me anyway! :P
If thats not an option anymore, perhaps just going out for a walk for a bit? I know it sounds lame, but I think part of your being depressed is just not having anyone to talk to / being cooped up in your house, so it might be worth considering just going for a jog for a bit? Wander around town? Or perhaps make an effort on your gaming adventures to have a chat to a friendly player (should you find one that is, it seems retarded bigots are all over the place these days)
Hope you figure something out, it's defo not a pleasant situation and I can totally relate, but now that i don't need to be taken care of when my parents go away, and if im back home from Uni, I just watch tv, play some games, go out with the friends if they aren't busy, and just take advantage of a free house with some loud music