sql 7 database replication

i am in the process of researching the best way to configure replication between our 4 branches connected by 3 slow analogue and 1 fast digital link. my prevois two tests have failed. i am using merge replication type and standard sql editions.
mydatabase does not have unique columns in all tables - and i need all the data in the table to be replicated in all branches.

what do i have to do to make the replication work? what are the issues to watch out for? is there a way of optimizing thereplication not to take so much of the bandwidth?