Rejected from 2nd yr bc of attendance

My brother was recently rejected from his second year A level equivalent diploma due to his attendance being 79% (school's policy is 90% minimum). His lack of attendance is in part due to our mother's stage 4 terminal cancer concerns as she is receiving specialised treatment abroad in Hong Kong and so he flies out when possible and thus has missed some school. On top of this we are not a well off family so he works part-time but is pretty much pushing full-time hours to fund himself (he's 18 yo) so I can imagine the exhaustion he must feel and mental stress on occasion which might cause him to miss school.

As his older sister I'd like to write to the college and appeal this decision so that he can complete his diploma and not jeopardise the rest of his life. I'm wondering if anyone has any advice on how to do this?