the problem in code here to enable display fileds from two table in gridview

con = new SqlConnection(str);
con.Open();
string custom_tb = "select branch_name,name,address,insurance_cost,record_date  from customers,branches where branches.code_branch=customers.code_branch ";
string branches_tb = "select * from branches";
string type_tb="select * from insurance_type";
dset = new DataSet();
da = new SqlDataAdapter(custom_tb , con);
da.Fill(dset, "customers");
da = new SqlDataAdapter(custom_tb, con);
da.Fill(dset, "branches");
da = new SqlDataAdapter(type_tb, con);
da.Fill(dset, "insurance_type");
builder = new SqlCommandBuilder(da);
dset.Relations.Add ("branches_customers",dset.Tables ["branches"].Columns ["code_branch"],
dset.Tables ["customers"].Columns ["code_branch"]);

dset .Relations .Add ("insurance_type_customers",dset .Tables ["insurance_type"].Columns ["code_type"],
dset .Tables ["customers"].Columns ["code_type"]);
dataGridView1.DataSource = dset.Tables["customers"];