In a joint tenancy, each tenant is liable for the rent for the whole property and the condition of the whole property. Each tenant will have a guarantor, so in theory, each guarantor is jointly liable for money owed to the landlord should any of the tenants or other guarantors not pay.
Unfortunately, some guarantors may not realise this. They may only think they are liable for the one tenant they know and are guaranteeing. However, in a joint tenancy, this is not the case.