To reproduce the problem:
two user accounts Mary and Peter
Peter created a patient and gives Mary all rights as collaborator (view, edit, permissions)
Mary creates a family with patient above in its pedigree
Mary sees the newly created family as her own
Peter does not see the family on the landing page (problem)
Peter can see this family if he goes to the Browse all families, where he can change the family, but not delete it (correct).
I think this is another manifestation of lack of proper rights management for families. Similarly to why we list all families in family list (including greyed out ones) - because that code assumes the collaborator pattern we use with patients, but we don't use it with families and use basic XWiki rights instead
we need to fix this for family-studies-m2, which will fix both issues.