3D grid tetris game problem!

Hi everyone, I'm doing a game base on Tetris idea. But I have a problem with block position. Basically, pivot of parent block is at center of one child block like image A, so all other child blocks will be positive position.

But I want it to rotate around centre on parent block so I move it like image B, so it will have 2 block with negative postion =>> will be wrong in grid check.

Here is my script:

Grid manager script:

public class GameManager : MonoBehaviour { public static GameManager instance;

 public int gridSizeX, gridSizeY, gridSizeZ;

 [Header("Blocks")]
 public GameObject[] blocksList;

 public Transform[,,] theGrid;

 private void Awake()
 {
     instance = this;
 }

 // Start is called before the first frame update
 void Start()
 {
     theGrid = new Transform[gridSizeX, gridSizeY, gridSizeZ];
     SpawnNewBlock();
 }

 // Update is called once per frame
 void Update()
 {
     
 }

 //Round block position
 public Vector3 Round(Vector3 vec)
 {
     return new Vector3(Mathf.RoundToInt(vec.x),
                        Mathf.RoundToInt(vec.y),
                        Mathf.RoundToInt(vec.z));
 }

 //Check position of block inside of grid?
 public bool CheckInsideGrid(Vector3 pos)
 {
     return ((int)pos.x >= 0 && (int)pos.x < 5 && (int)pos.z >= 0 && (int)pos.z < 5 && (int)pos.y >= 0);
 }

 public Transform GetTransformOnGridPos(Vector3 pos)

 {
     if (pos.y > gridSizeY - 1)
     {
         return null;
     }
     else
     {
         return theGrid[(int)pos.x, (int)pos.y, (int)pos.z];
     }
 }

 public void UpdateGrid(Block block)
 {
     //Delete possible parrent Objects
     for (int x = 0; x < 5; x++)
     {
         for (int z = 0; z < 5; z++)
         {
             for (int y = 0; y < gridSizeY; y++)
             {
                 if (theGrid[x, y, z] != null)
                 {
                     if (theGrid[x, y, z].parent == block.transform)
                     {
                         theGrid[x, y, z] = null;
                     }
                 }
             }
         }
     }
     //Fill in all child Objects
     foreach (Transform child in block.transform)
     {
         Vector3 pos = Round(child.position);
         if (pos.y < gridSizeY)
         {
             theGrid[(int)pos.x, (int)pos.y, (int)pos.z] = child;
         }
     }
 }

 //Spawn New Block
 public void SpawnNewBlock()
 {
     //Block Spawn Pos
     Vector3 spawnPoint = new Vector3(0, (int)transform.position.y + gridSizeY, 0);
   
     int randomIndex = Random.Range(0, blocksList.Length);

     //Spawn the block
     GameObject newBlock = Instantiate(blocksList[randomIndex], spawnPoint, Quaternion.identity) as GameObject;
     //Set Input
 }

}

And Block Script:

public class Block : MonoBehaviour { public static Block instance;

 float prevTime;
 float fallTime = .2f;

 private void Awake()
 {
     if (instance = null)
     {
         instance = this;
     }
 }

 void Start()
 {
     GameController.instance.SetActiveBlock(gameObject, this);
 }

 void Update()
 {
     if (Time.time - prevTime > fallTime)
     {
         transform.position += Vector3.down;     
         if (!CheckValidMove())
         {
             transform.position += Vector3.up;
             enabled = false;
             //Create a new tetris block
             GameManager.instance.SpawnNewBlock();
         }
         else
         {
             //Update the grid
             GameManager.instance.UpdateGrid(this);
         }
         prevTime = Time.time;
     }
 }

 public bool CheckValidMove()
 {
     foreach (Transform child in transform)
     {
         Vector3 pos = GameManager.instance.Round(child.position);
         if (!GameManager.instance.CheckInsideGrid(pos))
         {
             return false;
         }
     }
     foreach (Transform child in transform)
     {
         Vector3 pos = GameManager.instance.Round(child.position);
         Transform t = GameManager.instance.GetTransformOnGridPos(pos);
         if (t != null && t.parent != transform)
         {
             return false;
         }
     }
     return true;
 }

 public void SetRotationInput(Vector3 rotation)
 {
     transform.Rotate(rotation, Space.World);
     if (!CheckValidMove())
     {
         transform.Rotate(-rotation, Space.World);
     }
     else
     {
         GameManager.instance.UpdateGrid(this);
     }
 }

}

Anyone have ideas to fix this for me please! Thank you very much!