All four of the players have signed two-year contracts with Rovers until the end of the 2015 season.
Flanagan, 26, ironically scored the golden point winner in Batley’s recent play-off victory over Featherstone, as he enjoyed his most productive year to date in 2013.
The former Bradford hooker scored 14 tries last season and incoming Rovers head coach John Bastian had this to say: “George is a larger than life character and will bring lots of enthusiasm to our squad.
“He is extremely dynamic from dummy half, and I feel that Andy Ellis and George will be a key facet of our side in 2014 and beyond.”
The former Leeds, Halifax, York and Wakefield half-back was virtually an ever present for Batley last season, the club with which he tasted Northern Rail Cup glory with in 2010.
“Gareth has a very strong kicking game which I am sure Rovers fans witnessed in games he has appeared against us recently. Gareth also has a very good passing game and importantly is very vocal and a very good organiser on the field.
“He has aspirations that match our own to play at a higher level and I feel we can fulfil Gareth’s ambitions at Rovers.”
Hirst, 25, has experienced Championship rugby at Hunslet and Dewsbury as well as Batley, whilst Walmsley, the brother of St Helens forward Alex, previously played for National Conference outfit Dewsbury Celtic.