Now, before I dive into this, know that I've already thought this through and can think of no reasonable solution. SInce the Escapist is usually a friendly, helpful place, and least with regards to the rest of the horrifying monstrosity that is the internet, I've decided to ask you for help
This is pretty bad sh*t. (By the way, before reading the topic I assumed that it was the usual type of "friend" with a problem, but you don't sound like you're from an Islamic fundamentalist family.)
The fact that your friend is under such tremendous pressure and already cutting himself essentially means that he can't cope in a normal way with his parents' expectations and control over his life. The fact that the parents have continued their behavior, while other siblings and relatives have broken off from the family as a result, is a strong indicator that they are not going to change, listen, or be open to reason.
If your friend were inclined to be more secular and savvy about it, he could do the old good boy/bad boy routine and just fake it with them. This is the standard, historically proven trick/coping mechanism for strict religious parents, regardless of the religion. In other words, just don't get caught. (This also works for a large number of Saudi adults, as the facade of piety is forcibly kept up while in Saudi airspace, but once they get out, watch out.) From your description, though, I have some doubts about your friend's willingness and/or ability to do the split personality act. If he wants to have a life of his own and also maintain relations with his parents, however, I don't see another option. This approach also involves a good deal of stress, but I wager that a conscious decision to internally follow your own path, yet show filial respect where it is expected, is a lot better than feeling lost and confused.
The place your friend could go for outside help with his situation would be his older siblings. They may have broken ties with the family, but they went through the same thing and are at least likely to be sympathetic, since they have been in your friend's shoes. Why not track them down and hook your friend up with them for a talk?
Finally, I suggest checking the policy regarding school psychologists/counselors. In the U.S., they are normally required NOT to tell parents about counseling sessions (especially when the parents are the problem). Since you're in the U.K., not sure what the applicable laws are.
Good luck and best wishes to your friend.
All I can say is, be there as much as you feel you can for your friend. I'm really drawing a blank on this one, I'll ponder it and come back if I can think of anything else helpful, sorry buddy.
Do you think that your friend can contact his older siblings for advice? Ask them what they would have done differently to at the very least make their lives less of a headache? Perhaps they could show their support for your friend's less strict attitude/behavior in front of his parents? I think the best solution is to set up a family intervention of some sort considering the parents are driving all of their children away. I cannot predict how serious the siblings are about "breaking ties" and whether or not they broke ties with your friend as well, but pretty much the idea Carlo One expressed about his siblings, but I'd also extend it to his cousin. Perhaps even less strict friends of the family?
Is your friend old enough that his parents cannot really force him to go to Kenya? Did his parents force that onto his siblings or ever threaten to? Does your friend have a single point of leverage on his parents to show them that the society they now live in is NOT actually corrupting? By that I mean, do the parents actually really like or appreciate anything about the new culture they find themselves in?
How old is your friend now? Self harming is something you need to make sure he WON'T do. I won't start a whole religious scene here, but at +18 he needs to realize HIS life belongs to him, not his parents, not a deity. HIM.
Try to get him to see a Doctor or councillor (one with both an open mind and isn't too religious) to help him. Although I can't tell people to just disown your god, but there comes a point in life where YOU as a person need to make the decision on where you want to go with life, spiritual or otherwise.
needless to say, although I don't follow a god, nothing is worse then someone shoving their beliefs down someone else's throat, god or otherwise.
I agree with everyone who's said to contact the siblings. It sounds like they're probably the best place for him to get support right now. Though without knowing his legal standing (is he an adult or not?) it's hard to say what the best course of action is.
Talking to the school councilor sounds like a good idea as well, provided the counselor won't be obligated to talk to the parents. Finding out their kid is seeking counseling could just scare them more.
Does the family have a mosque they attend? If so, your friend might try explaining the situation to the imam (I'm assuming the imam functions similarly to a priest--I don't know much about Islam). If he's a more level-headed individual, and someone the parents respect, then he may be able to explain to the parents that they're causing more harm than good by driving all of their children away.
As for the cutting, I don't think there's much that can be done about that until the larger issue is resolved. The fact that he's cutting his shoulder is good, though--he's not likely to do any major damage if he sticks to that area. Don't try to pressure him to stop, and don't be judgmental about what he's doing. Just let him know you're there for him if he wants to talk. Speaking from personal experience having someone to talk to about self-harm, who you know will listen without judging you, is enormously helpful.
I would recommend what everybody above me said.
If I can add to the discussion, I've self-harmed myself quite a bit so I can give you some advice you could tell him.
I'll start by saying that if he self-harm, it's probably because he too feel out of option, if he feels cornered it's because he tried to get himself out of the situation, sadly in vain.
I will say: don't pressure someone to stop self-harming, it won't change anything. At this point, more pressure is something your friend wouldn't want to deal with. Try to understand him instead, ask him what motives led him to do such act.
Now if I could give him advice, tell him that there's alternative to self-harming. A method I used that worked a couple times was by submerging my head under really cold water for a couple second. It really helps clear the mind.
Now if the trick doesn't work and he continue to self-harm, try to convince him to go see a professional alone. Anything would do: a doctor, a psychologist, a social worker, a psychiatrist etc. Self-harming is definitively a sign of some mental illness and shouldn't be ignored.
Also I really hope he at least disinfect his wounds after self-harm (he'll enjoy the pain of doing so anyway) and he cut himself with a clean blade as the chance of infection could be high. Also tell him that if he have to do it, doing it on the hip is more discrete and less risky.