My best friend at the times mom died back when I was like 17 and it was so hard
Basically be their rock, be there for them, understand that they will prob act weird - don't get mad about it, check on them every day, take them on long rides and just let them cry, if y'all are really close then let them cry
Idk man it's so hard but like we got so close because of how supportive I was idk it sucks honestly