What to do with an unruly younger brother?

Well first some back story. I am the oldest of 4 (I’m 25). My younger brother, Dan, is the 3rd child. Our mother fought cancer for 11yrs before passing away March of 2010. It was very hard on our whole family. My dad went over the deep end religiously to cope. Like over night from slightly Christian to total zealot. So Dan is 16 now, only him and my 13 yr old sister are left at home. And Dan will not behave. Fakes being sick all the time and misses school, won’t do any work around the house unless you monitor him every second. Last semester he missed something like 50 days of school. Some weeks he would only go Monday when my dad has off, and go back to bed the other days since my dad leave for work just as Dan is getting up.

My mother was really the one behind the discipline in our house. My dad has always been very poor at it. So he doesn’t follow through with disciplining my brother. My dad doesn’t beleieve in physical punishment any more, so just try got ground Dan, but its had to enforce all the time when my dad has to work 7-4 Tues thru Sat. Sundays he goes to church in the morning, most of the time both kids go with him, then he goes to these college classes for something to do with church, then to the evening service. So Saturday the two kids (16 & 13) are home unsupervised. I feel they are old enough not to need constant supervision, just direction. And Sunday he isn’t home much. Monday when he is home kids are at school, and the rest of the week they get home an 1hr before he does.

Ok I know I’m rambling but I’m worried mostly about Dan. He gets very poor grades, doesn’t go to school, doesn’t do any work around the house, and sits and watches TV and plays on the computer. 2 more yrs and he is 18 - an adult! I worry that he is just going to fall through the cracks in society. My grandma tries to help, but to my dad she is the “mother-in-law” and they have never been on very good terms. His mom is pushing 91 and can’t do anything really. I just don’t know what to do to help get my brother Dan motivated. I try to talk to him over the phone and stop by some, but I have my own life too. Full time job, own my house, and im busy. So I can’t been there all the time to do what my father should be doing.

HELP!