A study of $ {\Lambda}b^0 $ and $ {\Xi}b^0 $ baryon decays to the final states $ p{K}{\textrm{S}}^0{\pi}^{-} $ and $ p{K}{\textrm{S}}^0{K}^{-} $ is performed using pp collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb − 1 . The decays $ {\Lambda}b^0\to p{K}{\textrm{S}}^0{K}^{-} $ and $ {\Xi}b^0\to p{K}{\textrm{S}}^0{K}^{-} $ are observed for the first time, with significances reaching eight standard deviations. The branching fractions and integrated CP asymmetries are measured for the $ {\Lambda}b^0\to p{K}{\textrm{S}}^0{\pi}^{-} $ , $ {\Lambda}b^0\to p{K}{\textrm{S}}^0{K}^{-} $ , and $ {\Xi}b^0\to p{K}{\textrm{S}}^0{K}^{-} $ decays. For the decay $ {\Lambda}b^0\to p{K}{\textrm{S}}^0{\pi}^{-} $ , the CP asymmetries are measured in different regions of the Dalitz plot. No evidence of CP violation is observed.