Tenants may indeed have multiple guarantors to support their application if desired. This includes individuals and guarantor companies.
Guarantors will be asked to sign the same tenancy agreement as the tenants, and so each become legally liable to cover the whole rent and/or the cost of damage to the property if the tenant fails to do so. Guarantors need to be UK residents and we always advise that they are comprehensively referenced alongside the tenant to ensure they are suitable. Please note that we are unable to reference guarantor companies.
In our referencing assessment, the affordability of multiple guarantors can be combined. However, guarantor affordability is not combined with tenants' affordability.
Most tenancies in the UK are created as Joint Tenancies (whereby several parties are named on one agreement) and it is important to note that this will mean that all parties are jointly liable for all the obligations named in the agreement. This means that any one tenant or guarantor can be asked to pay the full amount owed by any or all of the other people named on the agreement, if necessary.
More information:
What is a guarantor? What do they have to do?
How do I add a guarantor to my tenant's referencing application?