Complex sentence: Luigi Ossoinack had a decisive influence on the political life in Fiume, being the principal financial supporter of the fiuman Autonomist Party and both of its leaders Michele Maylender and Riccardo Zanella were actually his employees.
Split into simpler sentences: Luigi Ossoinack had a decisive influence on the political life in Fiume, being the principal financial supporter of the fiuman Autonomist Party. Both Autonomist Party leaders Michele Maylender and Riccardo Zanella were actually his employees.