We consider a U(1)′ extended supersymmetric model with a right-handed neutrino superfield which can generate light neutrino mass by Type I seesaw mechanism. The lighter superpartner of the right-handed neutrino could be the scalar dark matter. These right-handed sneutrinos can come from the decay of Z˜ ′, superpartner of the extra gauge boson Z′. Left-right handed sneutrino mixings affect their decays further, giving rise to displaced “lepton flavour violating” signatures. A wino-like chargino NLSP (next to lightest supersymmetric particle) creates even more interesting decay topology. We investigate such displaced multi-leptonic final states with “lepton flavour violation” from the supersymmetric cascade decays of third generation squarks at the LHC. © 2017, The Author(s).