You add a guarantor to a deal by ‘right-clicking’ the treeview on the guarantors tab of the deal screen.
It is important to remember that, in law, a guarantor does not guarantee any one tenant. As the tenants are "jointly and severally liable" a guarantor becomes liable for the entire amount claimed - that is the landlord or agent can pursue any one individual for the entire amount regardless of which tenant is deemed in breach of the agreement. It would be wrong to indicate that a guarantor is only liable for money owed by one tenant. You can, however, link a tenant to a guarantor in order that you know who to call first; go to the notes section of the tenant and select from the list of guarantors.
The Rentman standard agreements include a clause that limits each guarantor's liability to be the amount claimed divided by the number of guarantors on the agreement.
By default rentman will prevent you ticking the periodic checkbox on the deal screen when there are guarantors on the deal. Our legal advice tells us that a Guarantor's obligations end at the full term of the original agreement and will not be extended by section 6 or section 13 notices…. ... but there is an option on the Company Preferences screen if you have your own legal advice and want to allow it.