Collect[Expand[(((w+x+y+z))^5)], {y,z}]

Collect[Expand[(((w+x+y+z))^5)], y|z]

Collect[Expand[(((w+x+y+z))^5)],z|y]

Collect[Expand[((((Subscript[x, 1])+(Subscript[x, 2])+(Subscript[x, 3])+(Subscript[x, 4])))^5)],(Subscript[x, k_])/;k≥3]

Total[CoefficientRules[Expand[(((w+x+y+z))^5)], {y,z}] /. (ps_->c_) :> c (Times@@(({y,z})^ps))]