Master detail Problems

Hy there,

        I've run into a slight problem that i think is due to my lack of
knowledge:
        - I'm working with delphi 3.0 server/client suite, interbase databases.
        - Here's the schematics of the problematic master/detail tables:
                create table groups (groupid integer not null primary key,description
string);
                create table famalies (groupid integer not null,
                                        famid integer not null,
                                        description string,
                                        primary key(groupid,famid));
                create table subfamalies (groupid integer not null,
                                        famid integer not null,
                                        subfamid integer not null,
                                        description string,
                                        primary key(groupid,famid,subfamid));
        - SubFamalies is a detail of famalies and famalies is a detail of
groups.
        - Having 3 TDBLoockupComboBox's and the master/detail propertys of the
the 3 TTable quite correct
        i want to put groupid, famid and subfamid on the products table.
        - The problem arouses when:
                - after selecting group, familie and subfamalie by this order if i
want to change
                famalie it reports a "Record not found" exception...

        - I've tried to write an OnCloseUp event handler for each combo to edit
the fam and subfam key,
        in order to refresh the pointer of each table but it doesn't seam to
have any efect...

        How can i make the fam and subfam combos refresh to reflect any change
on the parent combo,
that is my main problem...

        Many thanks in advance !!!

        Gustavo Carreno