You do not need to reach a specific level to unlock the other two pieces of gear from each of these Amiibo, but there are additional steps you need to take to get them
The first time you use your Pearl Amiibo, you will receive the "Pearlescent Crown." Likewise, you will receive the "Marinated Headphones" the first time you use your Marina Amiibo. You will notice that they do not give you the additional gear if you try to immediately scan them into the game again.
To unlock the other pieces of gear from each Off the Hook Amiibo, you must first save an outfit loadout to the Amiibo.
To do this, press the + button on your Switch controller while in Inkopolis Square to bring up the main menu. Now go all the way to the last tab on the right. Under the Other tab, select the Amiibo tab. You will be able to choose your desired loadouts to save to the Amiibo.
Once you have saved an outfit to the Amiibo, scan the Amiibo at the giant Amiibo box in Inkopolis Square once more. You will now receive the other two pieces of gear for that Amiibo (the "Pearlescent Hoodie" and the "Pearlescent Kicks" for Pearl and the "Marinated Top" and the "Marinated Slip-Ons" for Marina.) You will also receive new themes and sound effects for Squid Beatz 2 from the Pearl and Marina Amiibo. Repeat the process with the other Amiibo to unlock her unlockable gear.