Groundlings Theatre in Kent Street, Portsea, was devastated in September 2019 leaving an insurance claim of £30,000 for the struggling theatre.
Doors and computers were damaged in the raid that saw five computer servers, two iPads, a laptop, a safe and £880 in cash stolen.
Then owner Richard Stride said damage done came close to shutting down the 236-year-old theatre.
Brothers Steven and Daniel Storey were charged by police with burglary and were due to appear before magistrates in August last year - with the case subsequently victim to a number of delays.
But on Friday the pair appeared at Portsmouth Crown Court.
Steven Storey, 40, of Hawke Street, has now admitted a charge of burglary.
Daniel Storey, 39, has also now admitted burglary - but on a basis of plea that was rejected.
Prosecutor Janice Brennan said: ‘(Daniel Storey) says other burglars were there who went in and took things and he and his brother came in later.’
She added: ‘This is not accepted by the Crown. This would make a significant difference to sentencing.’
A Newton hearing to decide the facts of the case will now be heard on December 23 with sentencing for both defendants due to follow.
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Daniel Storey was given an electronic tag and curfew of 9pm to 6am to reside at his Fawcett Road, Southsea, address until the hearing.