This article presents a new set of proton parton distribution functions, ATLASepWZVjet20, produced in an analysis at next-to-next-to-leading order in QCD. The new data sets considered are the measurements of W⁺ and W⁻ boson and Z boson production in association with jets in pp collisions at s = 8 TeV performed by the ATLAS experiment at the LHC with integrated luminosities of 20.2 fb⁻¹ and 19.9 fb⁻¹, respectively. The analysis also considers the ATLAS measurements of differential W^± and Z boson production at s = 7 TeV with an integrated luminosity of 4.6 fb⁻¹ and deep-inelastic-scattering data from e^±p collisions at the HERA accelerator. An improved determination of the sea-quark densities at high Bjorken x is shown, while confirming a strange-quark density similar in size to the up- and down-sea-quark densities in the range x ≲ 0.02 found by previous ATLAS analyses. [Figure not available: see fulltext.]