As someone who has lost a stepdaughter and an "adopted family member", who we actually took in for a while, at various times, while I can say I'll never be able to fully understand the effects of your grief and that of your family and that of the girl who died, I have felt high-magnitude grief and have seen its effects on myself those around me.

Be strong, finding strength within yourselves and reach out and find it from what other human and spiritual sources are available as needed. Keep a knowledge of what the others are going through in order to get through it on a family as well as an individual level. My thoughts are with you as well.