Trust query

My father died a few years ago and in his will he left his share of the property in trust to myself, my sister and the grandchildren. It was his second marriage and we have no contact with his very elderly wife and her family. How can I check if the trust was registered as she became the sole trustee on his death and we don’t know whether she is still alive or whether the property has been sold without us knowing? An added complication is that between them they only owned 70% of the property as it is part owned by a housing association, it being a retirement complex. 

Philip - we don't specifically register 'trusts' and I would recommend that you start by checking if the property is registered and if so to whom and how - Search for land and property information - GOV.UK