There is no way in hell that your friend should be doing GOMAD; that prescription is only relevant for people with super fast metabolism a who have legitimate trouble gaining any weight (and even then I personally would only recommend it as a last resort). Your friend clearly does not have trouble gaining weight though.
What he does seem to have trouble with is will power and consistency. Unfortunately for him it seems like his family is a major contributing factor in this and he will likely have to deal with making them unhappy (or possibly even separating himself from them completely for a little while) to overcome if he ever hopes to achieve his physique goals.
He needs to decide that the long term happiness/satisfaction/self esteem of achieving his goals is worth the temporary discomfort of denying himself junk food and making his family unhappy that he isn't re-enforcing their unhealthy food habits.
Once he actually starts to eat a healthy, nutrient rich, balanced diet he should start to see some noticeable changes in not only his physique, but also his energy levels, and his general mood/sense of well being.
As far as the program goes, I would not recommend he do SS. Yes, it does an ok job of teaching and emphasizing the basic power movements (squat, bench, and deadlift), but there is not enough emphasis put on the smaller muscle groups. In short SS is a strength program, not a physique program.
I actually would advise him to stick with a body part split, but to make sure that (at least) the first movement of each day is a heavy compound movement which uses a lot of muscles and will help him to continue to increase his strength for the "accessory" exercises that follow.
Have him check out CT's article "How To Design A Damn Good Program" (there are two parts) for a basic template (I'd suggest he picks one of the "size/hypertrophy" templates as that will build the most muscle, which will in turn change his shape as well as raise his resting metabolic rate.