all, both, few, most, several, some etc. + of + whom/which

Her sons, both of whom work abroad, ring her up every week («Both her sons work abroad, but they ring her up every week»). He went with a group pf people, few of whom were correctly equipped for such a climb («He went with a group of people; few of them were correctly equipped for such a climb»). The buses, most of which were already full, were surrounded by an angry crowd («Most of the buses were full, and/but they were surrounded by an angry crowd»). I met the fruit-pickers, several of whom were university students («I met the fruit-pickers; several of them were university students»). I picked up the apples, some of which were badly bruised («I picked the apples; some of them were badly bruised»). The house was full of boys; ten of whom were his own grandchildren («The house was full of boys; ten of them were his own grandchildren.»)

[Esta fórmula puede aplicarse tanto a personas como a cosas. En cada caso el ejemplo entre paréntesis añade un equivalente más informal.]