At times like this, the law is of very little assistance.
You MUST get on to this immediately. All the forms (10 Day Notice to Remedy, application for Tenancy Tribunal) are all on-line.
I would fill out 10 day letter and personally hand it to tenant. You can apply for Tenancy tribunal On-line.
Do not sign over the Bond to them, that way you have at least three weeks rent as a buffer. You will probably be out of pocket for cleaning, rubbish removal, lock changes etc.
Which is why some of us older, wiser LL's ask for the maximum bond (four weeks) so that there is even more buffer if the tenants turn idiots.
Also you may get your lawyer to send a letter to them loosely "scare them off"