Reverse relationships with entries and users
{% set people = craft.users.group('family').ids() %}
{% set relatedPlaces = craft.entries.section('locations').relatedTo({
    targetElement: person,
    field: 'relatedPeople'
}) %}


Grab all the ids from your users, then find all locations related to those. This way you don't need multiple loops and get each location once and not multiple times