[candidate_parameters] Family tab add functionality appears to be broken

[HachemJ]

Describe the bug
When testing the Family tab changes, I noticed that adding a new relationship using the Add button fails on the main branch (consequently on my FixFamilyTabLabelsFromSQL branch #10510 that was fixing another issue)

When attempting to add a new family relationship, I get the following error in the console Uncaught TypeError: familyMembers.push is not a function

To Reproduce
Steps to reproduce the behavior (attach screenshots if applicable):

1. Go to the Family Information tab. (The Candidate parameters module is reachable by going to access profile (candidate_list) --> click on a candidate --> click on candidate info).
2. (Optional) In some cases the Family tab is unaccessible if the study configuration does not have it enabled (check config module). You can also enable it from going to Admin --> Configuration --> select useFamily --> Submit.
3. After opening the console, for a given candidate, choose a candidate id from the family member ID (DCCID) dropdown then choose a relationship type from the Relationship Type dropdown.
4. See error

This picture has been taken from the main branch.

What did you expect to happen?
A new family relationship to be added successfully without the Uncaught TypeError: familyMembers.push is not a function error.