Here are some PS2 Game to PS4 PKG articles that may be of use:
PS2 Game Backups on PS4 HEN & Make_fself.py Update by Flat_z
How to Create Emulated PS2 PS4 Packages (PKGs) Guide by G991!
PS2 Classics GUI: Convert PS2 ISO to PS4 PKG by TheDarkprogramer & PS2 FPKG by JabuPL
How to Update...