Having Gizmo eating so many eggs for a joke was a bad move. Once would have been fine, because he doesnt know better, but after that it stops being funny and just becomes unpleasant.
I dont think Mando had much choice with the Xwing pilots. He was on a deadline, and if he cooperated with the pilots he would have been tied up with them for hours or days. And once they found out who he was he was looking at an arrest, trial, and imprisonment. The Child would have been taken into custody, and civilian caretaker wouldn't be equipped to protect him. He could have tried to explain the situation to the NR, but there's no reason for them to believe he is on the level and not just some money hungry criminal bounty hunter. At best the pilots would have agreed to escort him to the system to drop off the eggs after which they wpuld have tried to arrest him.