I want to know how a doctor can diagnose that a tumour is benign from an x-ray

No, as that would require a biopsy.

SO why are they refusing to do one. I want to be sure that it is HME and nothing else shoud they have done blood tests or something else as these tumours are growing quite fast and causing so much pain. His arm gets pins and needles and pain. And his leg goes blue and has extreme pain where he cries for hours on end after paracetamol and ibuprofen.