No licenses are required for your testers machines; however, i recommend installing the LoadRunner ''full setup'' on their local machines for creating script, debugging and small smoke tests, proof of concept testing and the free 50 Vusers community license.
IMPORTANT NOTE about the 50 free Vusers Community license ---
''LoadRunner 12.xx includes a community bundle license, limited in use for the purpose of test development and proof-of-concept execution. This community bundle includes all protocols except GUI Virtual Users. The community bundle is provided without support or warranty of any kind, and commercial use is strictly prohibited.'' (Micro Focus)
Happy testing