I would say have the son die since he would be the only reason as to why a rebellion would start in the first place. Leave Liviana out because she has enough reason to change whereas the son would be too driven by jealousy, hate, etc. to ever change.
does the plot thickens by the author decision to let the queen and her son live or it is just a pure mercy to them. I believe that mc will probably send souei to them later and ya know kill and end this.