The policy is being misapplied because this is obviously a bona fide course which will give its students employment potential in many countries. I looked for an online petition to the Home Office but none has been started yet, apparently. There is room for discretion in granting visas so a petition can have some influence. Recently two Syrian refugee brothers were seriously injured in the Grenfell fire; one of them died. I expect that public support, including a petition, influenced the Home Office decision to let the young men's parents come to the U.K. I do think the violin making course should be recognized for future Tier 4 student visas; after all it's in the U.K. school's own interests! But more immediately important, the four students from outside the E.U. who have already studied at the school for the past academic year should be given exceptional leave to remain while they complete their studies.
The article says that students have approached m.p.s but doesn't say what reaction they got ... maybe it's just to early in the day.