If you have the output datatable with the columns combined dt1 and dt2 you can use below LINQ to merge rows of two datatables side by side.
(From row1 In dt1.AsEnumerable()
From row2 In dt2.AsEnumerable()
Select dt3.Rows.Add(row1.ItemArray.Concat(row2.ItemArray).ToArray())).CopyToDataTable()