Hello ! Your first sentence "Une malédiction pèse sur vous" is completely correct in French. It means "to hang over". For instance : "There is a threat which hangs over us" : "Il y a une menace qui pèse sur nous". Your second sentence is not employed. To use "peser" in this way, you would say for instance : "Ca me pèse d'aller à ce congrès à Paris", "It is a really constraint to me to attend this congress in Paris". Here you are !