"There has been no activity on the account for 6 years and they haven't filed" = Don't file, if not need.

I believe that you may have a grantor trust, unless the trust was created due to the death of a joint tenant. You should definitely get a copy of the trust (or the will if it really is an estate). 

Before you start to freak out over penalties, you need to determine if you are able to complete a proper return. If so, is there a tax due and who is liable for the tax. If not, find a more capable preparer to refer the client to.