Why is the casino heist vehicle prep impossible to do solo?

I've tried to do it at least 20 times the past few days and just cannot figure out a way to get the motorcycles to my arcade. I've tried the sandking method i've tried stealing them from the police i've tried just bringing them back slowly one by one and i fuck something up or it goes awry every time without fail. i feel so defeated and at this point i'm just gonna wait for the new one to come out to maybe have actual people to play with cause this game is dry asf 💔🥲