Longer tenancies

Tenancy Types and Management

I have many tenats all of whom I consider to be reliable who I wish to provide with longer term security. Due to my past history they all feel safe but there would be issues like what would happen in the event of my death, but this is not the only example.
I have in mind granting 7 year assured shorthold tenancies with tenant break clauses every 3 months. Besides the obvious issue of me not being able to ask them to leave during the period except under s.8 conditions, what are the implications of this? I believe that the tenancy would need to be done under deed. Is this correct and can it be done without the costs of a solicitor?