Your post is not clear. You are the management company?
Don't whatever you do act illegally. I would contract the PRTB to see if the landlord is registered, there are options via the PRTB to force landlords to deal with anti social tenants, whether the landlords is registered or not, so I assume there may be another option where there is a danger to people.
I was recently in contract with the PRTB and was surprised at how quickly they picked up the phone and how efficiently they dealt with my registration issue, so maybe they are now a competant organisation and can be of help to you.
Alternatively, contact the landlord organisation, by phone, the IPOA, for advice.