You should be serving the tenant with a legal notice of nonpayment of rent which is a Form N4. This notice gives the tenant fourteen days to pay the outstanding rent, if it’s not paid within that time period then the next step would be to file an application with the Landlord and Tenant Board. The forms required to apply to the Board is a Form L1 and a Certificate of Service. The process at the Board can take up to four months to evict a tenant so it’s best not to wait too long to get the process started. These forms can be obtained from the Board’s website at https://tribunalsontario.ca/ltb/forms/#landlord-forms. As for the tenant having other people living there that are not on the lease, unfortunately there isn’t anything you can do about this, tenants are allowed to have anyone living with them despite what the lease states.