You can add a maximum of 1 Instagram account (Business/ Personal) to a Brand in Zoho Social. If you want to manage multiple Instagram accounts, you will have to set them up as separate Brands.
If you are publishing posts to multiple Instagram Personal Profiles with the mobile notification workaround, you have to make sure you are posting it to the right account.
Instagram lets you manage 5 active accounts per device. Also, make sure you don't opt in to remember your accounts' passwords so that you can log in to the 6th account. To log in to the 6th account, you will have to log out of all the other accounts.