The poor child has a Gr4 cancerous brain tumour Gr4 being the most aggressive, according to a blog by his brother.
Who knows what the parents are thinking but with an almost terminal diagnosis which may be imminent, maybe they wanted to take control of the inevitable and allow it to occur with all the family around in a setting of their choice.
I am sure if they had been happy with the treatment and the prognosis was improving, no loving parent would move their child, and these appear to be a loving family according to all reports.