Scott Snowden and Robert Jennings are accused of killing Thomas Sharkey, 55, his son Thomas, 21, and eight-year-old daughter Bridget at their home in Helensburgh on July 24, 2011. The pair are also charged with attempting to murder Mr Sharkey's wife Angela.
It is alleged Snowden, 37, and Jennings, 50, poured petrol through the letterbox of the Sharkey family home while they were asleep and set the liquid alight.
Snowden is said to have "envinced malice and ill-will" towards Mr Sharkey by threatening to shoot him and have his house burned down.
The pair are also accused of being involved in six other fires in Helensburgh, Rhu and Loch Lomond – including at three different pubs. Snowden faces a charge on his own that he started a fire at a construction site in July 2008.
The pair are also said to have offered someone drugs and money to throw ammonia into the face of a man at a Helensburgh bar in January 2011.
Snowden and Jennings pled not guilty to the charges at an earlier hearing.
Judge Lord Turnbull set the trial for April 30.