Obnoxious Neighbour

I am looking for advice on behalf of the Goldfields Repertory Club, we are facing problems from a neighbour who has made complaints to our City Council about Noise Pollution. Our Theatre has been in its present location since the 1940s or 50s and in 1998 the City Council approved a development of 8 units next door! Our Christmas show saw the Council Enviromental officer pay us two visits and in our current poduction we have had to endure rocks being thrown onto our roof, to celebrate opening night.
The GRC committee has asked me to investigate the options so we can better soundproof our Theatre. The original Theatre burnt down in the mid 70s and the present building started Life as an old Railways Shed I've been told. It has a Corrugated Iron Roof that is supported by large timber trusses and all that is between the stage and the outside world ( other than the Iron) is some dodgy Sisalation. My thoughts are to line with Chipboard and Insulation Batts or a more suitable material but am unsure of what will be best for the Soundproofing and the Acoustics for the auditorium. I dont want to make it soundproof to the outside and then find that the material is also damping the Actors Voices. The Theatre only seats 90 so we aren't talking about huge spaces. As a Community Theatre Group our budgets are also a big consideration.