OP I'm sorry to say it but you will have to make more of an effort with the dc. And it will be effort but you'll all benefit enormously
You need to find a way to help your dc who was bullied & has no friends. He needs friends. It's vital. What's he interested in? Start with him. Could he try skateboarding, there's probably a skate park somewhere & you could visit
Similarly wall climbing, bike riding, swimming, bodyboarding if by the sea, cooking, baking, go to a local match, dance class, exhibitions of stuff he's into - lego / manga, geocaching, pokemon hunting, treasure hunting, hiiking whatever!
Encouraging him to get stuck into life will be fantastic for the younger ones who will see this as the norm in their lives too
It will get you all out of the house & give you things to look forward to & give you all things to plan & discuss & a level of excitement.
Letting then sit around the house on devises or watching TV is not good for anyone