From my understanding, everything from the store is character based and not account based. I wasn't able to buy a Hireling on another character because I don't own a house but if you look at my two character's store summary the Hireling Jobs didn't get applied to my other character.
To get to your character's store summary just go to the Cyclopedia -> Character -> Store Summary!
HirelingsGet your very own NPCs and put them in your house. Every character can own up to 10 hirelings. Hireling Apprentice: If you purchase a Hireling Apprentice, it will greet you and your guests and sell you some basic items. At purchase, you will be able to select your hireling's gender and choose a name. Make sure that the name does not violate the Tibia Rules or you risk a punishment. In such cases, your hireling will be renamed automatically with some randomly generated name.Banker: If you purchase the apprenticeship Banker, all of your hirelings will allow you access to your Tibian bank or guild bank account with all known functionalities.Trader: If you purchase the apprenticeship Trader, all of your hirelings will sell and buy all those items, which are also traded in Tibia's cities. Moreover, it offers the assortment of the Tibian post clerks.Steward: If you purchase the apprenticeship Steward, all of your hirelings will give you access to your supply stash.Cook: If you purchase the apprenticeship Cook, all of your hirelings will cook useful food in exchange for a fee.
HirelingsGet your very own NPCs and put them in your house. Every character can own up to 10 hirelings.
Source: tibia.com manual / houses
Hireling jobs are linked to character, not the account. It's confirmed, you can have up to 10 Hirelings and they all will get jobs that you have already purchased.
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