ParallelDo[
  Subscript[A, i] =
    Sort[FindIndependentVertexSet[
      Subgraph[W1, Subscript[req, i],
       VertexLabels -> "Name"], {Length[
        FindIndependentVertexSet[
          Subgraph[W1, Subscript[req, i]]][[1]]]}, All]];
  , {i, 3, 5}]]

I already defined statesArray2, Subscript[A, i],Subscript[req, i],W1 as follows:

For[i = 1, i < Length[statesArray2] + 1, i++,
  DistributeDefinitions[Subscript[req, i]];
  ];

DistributeDefinitions[statesArray2];

For[i = 1, i < Length[statesArray2], i++,
  DistributeDefinitions[Subscript[A, i]];
  ];

DistributeDefinitions[W1];