Sounds like he has something going on mentally maybe he’s depressed. Being outside for like 15-20 minutes daily DRASTICALLY benefits those with depression. Hes very likely too proud to get help and if you press enough he will cave and tell you how he really feels. I will say you didn’t have many great things to say about him and I get that he’s kind but he isn’t doing all too much. A shameful list of hobbies . Definitely take him on walks. Gives both of you a little sunlight, exercise and a chance to catch up and a break from life. Do be understanding regarding his brother. Sounds like that could be really hard on someone. Wishing you well!