We systematically revisit the baryonic four-body semileptonic decays of B−→BB¯′ℓ−ν¯ℓ by the perturbative QCD counting rules with B representing octet baryons and ℓ=e, μ. We study the transition form factors of B−→BB¯′ in the limit of (pB+pB¯′)2→∞ with the three-body B¯→BB¯′M and B−→pp¯μ−ν¯μ data along with SU(3)f flavor symmetry. We calculate the decay branching ratios and angular asymmetries as well as the differential decay branching fractions of B−→pp¯ℓ−ν¯ℓ. In particular, we find that our new result of B(B−→pp¯ℓ−ν¯ℓ)=(5.21±0.34)×10−6, which is about one order of magnitude lower than the previous theoretical prediction of (10.4±2.9)×10−5, agrees well with both experimental measurements of (5.8−2.3+2.6)×10−6 and (5.3±0.4)×10−6 by the Belle and LHCb Collaborations, respectively. We also evaluate the branching ratios and angular asymmetries in other channels of B−→BB¯ℓ−ν¯ℓ, which can be tested by the ongoing experiments at LHCb and Belle-II.