Scott Snowden and Robert Jennings are accused of killing Thomas Sharkey, 55, his 21 year-old son Thomas junior and eight year-old daughter Bridget at their home in Helensburgh on July 24 2011.
A preliminary hearing today called against the pair at the High Court in Glasgow where they faced an indictment featuring 22 charges.
The murder allegation includes a claim that petrol was poured through the letterbox of the Sharkey family home while they were asleep and the liquid set alight.
Thomas junior and Bridget died before their father lost his life in Glasgow's Royal Infirmary on July 30 due to his injuries.
It is also alleged they attempted to murder Mr Sharkey's wife Angela - the children's mum - during the same blaze at the property in Scott Street, Helensburgh.
Snowden, 37, is said to have "evinced malice and ill-will" towards Mr Sharkey in the months before the fire by threatening to shoot him and have his house burnt 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.
Snowden and 50 year-old Jennings 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.
Other allegations include a charge that Snowden threatened to set fire to a woman's house while she and her child were inside.
Snowden was not present during the hearing.
His QC Donald Findlay lodged special defences of incrimination and alibi in his absence.
Mr Findlay said the case was "one of some substance" taking into consideration the amount of charges involved.
Judge Lord Turnbull set a trial for April 30 at the High Court in Edinburgh.
It is expected the case will last several weeks.