A family is taking part in a walk-a-thon.
The family is taking place in the event in memory of another family member.
The family might just enjoy taking part of a walk-a-thon and not necessarily doing it in memory of a another family member.
The fact that a family is taking part in a walk-a-thon doesn't imply that it is an event in memory of another family member.
not every person participating in the walk-a-thon is doing so in memory of another family member