Mitchell happy to help here,

Facebook – add the person taking over the “side-hustle” page within business manager, detailed instructions here.

Instagram – you can add the linked account to facebook to allow the same user to manage that account.

Twitter – you should be able to change the email for the “side-hustle” account. You can verify with a 2nd email you own before transferring to the new person to make sure it doesnt try to assign that as the email to all of your accounts.