You can join Hive queries in Apache Nifi but I would suggest you not to as it is a difficult process and inefficient.
If you want to join regular queries in Hive, use those normal Hive processors(PutHiveQL, PutHiveStreaming, and SelectHiveQL) as usual with join queries statements. But if you join different regular queries in, it is irrelevant. Nifi is not used for joining Hive queries, It is almost impossible to do that in Nifi. (It is only possible using MergeSort and MergeContent processors and that is a very difficult process)