I'm surprised to find Nicola Spagnolo among the many witnesses the prosecution wanted to testify in a preliminary phase of Sal Montagna's murder trial. Spagnolo may have been either friendly with or hostile to Montagna--in my opinion only, very likely the latter.
The contract that Spagnolo is reported to have on his head probably has to do at least in part with his desire to avenge his father's death. The same might also be said about the imprisoned Liborio Cun-trera. But this assumes that the sons even know who was behind or directly involved in their fathers' murders.