Has anyone checked out his gull bladder for stones, his kidneys for stones and pancrease and/or appendix?
It wouldn't hurt to have those scans completed and maybe that would help uncover something. I don't really think based off those labs the parathyroids are causing him these issues.
What was the reference range for the PTH and calcium?
Have there been any regular thyroid tests done on your grandson? The parathyroids have no relationship to the thyroid gland, except for the location in the body. Throat pain when swallowing and the night sweats and the leg pain could indicate a thyroid condition. Where is the pain when he eats spicy foods? That could be a gall bladder issue.
The tests he needs to check thyroid function are TSH, Free T3, Free T4 and thyroid antibodies, Thyroid Peroxidase Antibodies (TPOab) and Thyroglobulin Antibodies (TGab). A thyroid ultra sound would also be in order.