Two primary key fields/Unique Index problems

We are working in Access 2000. Our database has three tables: People, Emails,
and Volunteer Data. The People and Emails tables (both have data in them)
have been imported from another database and are related by two primary key
fields: a family number and an individual number. We added the Volunteer Data
table in access and have included fields for the family number and individual
number as well as fields for all the volunteer information we need to track.
We’ve created a query and built a form off that query that allows us to pull
up a name (using the filter by features), and then we can enter the volunteer
information for that person. Our problem is that all of the volunteer info is
being saved, but we have been unable to populate the Family # and Individual
# primary key fields for the Volunteer Data table, meaning our data is there
but it is not associated with any record. So when we pull up a record for
someone we’ve already entered, the volunteer data is blank. How do we
populate those fields in the Volunteer Data table? We’ve tried working with
the relationships but we are getting a unique index error that we don’t know
how to get past due to the two primary key fields. The family # is unique to
each family, so there will be duplicates. Each family member has a unique
individual #. We’ve thought and thought and can’t get anywhere. We hope this
is enough information to give someone an idea of what we are trying to
accomplish.