family issues

Basically i wanted to ask you all some advice, i cant be too specific incase any of the people involved are reading this (unlikely but possible). The problem is my extended family on my dads side. His sister is a single mother of 2, eldest is 18, younger one is 15. The sister has spent the last few months in and out of hospital (mental health problems), the eldest has been living alone at the family home and the younger with his father. Anyway to cut a long story short the eldest is going to be spending xmas with her partner and his family, the sister remains in hospital and the younger kid plans to spend it with his mate and his family (not the kind of people you would want a kid to be with as they are involved with drugs etc) as he has left his fathers home. My mom and dad are trying to persuade him to spend christmas with us or dads other sister but hes not the kind of kid to open up, any tips on trying to communicate with him? Sorry this is such a long post - its very complcated! Thanks x