The　seismic　engineering　demand　parameters　(EDPs)　of　building　clusters　exhibit　significant　spatial　correlations　and　need　full　consideration　in　regional　risk　and　reliability　assessments.　This　study　presents　an　efficient　scheme　to　determine　the　joint　distribution　of　multi-structure　EDPs,　which　captures　all　EDP　correlations　and　enables　direct　calculation　of　system　reliability　for　building　clusters.　This　scheme　generates　spatially　correlated　random　ground　motion　fields　through　ground　motion　cross　power　spectrum　density　(PSD)　models　with　stochastic　harmonic　function　simulations.　Subsequently,　the　decoupled　multi-probability　density　evolution　method　(M-PDEM)　is　integrated　to　conduct　seismic　analysis　of　building　clusters　under　random　ground　motion　fields　to　determine　their　EDP　joint　distribution.　An　example　of　three　linear　single-degree-of-freedom　(SDOF)　models　shows　that　the　proposed　scheme　requires　only　hundreds　of　analyses　to　achieve　the　same　accuracy　as　10(5)　Monte　Carlo　Simulation　(MCS)　analyses,　while　also　capturing　the　nonlinear　correlations　among　EDPs.　Finally,　an　engineering　application　of　three　reinforced　concrete　(RC)　frame　shear-wall　buildings　under　a　rare　earthquake　scenario　is　investigated,　and　the　joint　collapse　probability　by　the　scheme　is　compared　with　that　by　commonly-adopted　assumptions　of　mutual　independence　and　linear　correlation.　The　results　reveal　that　relative　errors　by　the　two　assumptions　can　reach　up　to　39　%　and　22　%,　respectively.