Query of multi-valued field
This is a typical situation in which you have to create three tables: Helpers, Contacts, and Help_Contact, using the third table to represent associations between the elements of the first two, by storing the foreign keys for the first two, without any multivalued field in those.

That is, you should have something like:

Helpers(h_primary_key, other_fields_only_relevant_to_helpers)
Contacts(c_primary_key, other_fields_only_relevant_to_contacts)
Help_contact(h_primary_key,c_primary_key)


So, to display information for contacts or helpers associated to another element, you could use a join:

SELECT relevant_info
FROM Helpers h, Contacts c, Help_contact hc 
WHERE hc.h_primary_key = h.h_primary_key AND hc.c_primary_key = c.c_primary_key AND other_conditions_on_helper_or_contact_or_both