The men were first indicted Feb. 9 on 20 counts of first-degree murder. Firefighters discovered the bodies inside the family's rented home after it was reported on fire Jan. 19.
Authorities have said Serrano and Gilleo were partners with Manuel Morey in a small drug dealing operation.
Police said Serrano and Gilleo went to the family's home to attempt to steal illegal drugs, and during the robbery Tony Morey and his wife were shot and the three boys were stabbed. Attorneys for Serrano and Gilleo could not be reached late Thursday.
The new murder charges include five counts of intentional murder and six counts of felony murder causing someone's death while committing another felony.
Second-degree murder carries a maximum sentence of 25 years to life in prison. The first-degree murder charges are punishable by life in prison without the possibility of parole. Both men are being held without bail.