Generate a grid button

Hello everybody, I want create a Chomp Game on Unity : https://en.wikipedia.org/wiki/Chomp

My idea was, create a button grid without gridlayout because the buttons are replaced each time a button is removed. So i made a code to instantiate with x and y many buttons.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class terrain_generator : MonoBehaviour {
 
     public GameObject deathButton;
     public GameObject simpleButton;
     public GameObject terrain;
     GameObject death;
     GameObject clone;
 
     public int x;
     public int y;
 
     public Button[,] GameGrid;
 
     void Start () {
 
         x = x * 25;
         y = y * 25;
 
         GameGrid = new Button[x,y];
 
         
         death = Instantiate(deathButton, new Vector3(terrain.transform.position.x, terrain.transform.position.y),Quaternion.identity);
         death.transform.SetParent(terrain.transform,false);
 
 
         for (int i = 0; i< x; i = i +25)
         {
             for(int j = 0; j < y; j = j+25)
             {
                 
                 clone = Instantiate(simpleButton, new Vector3(terrain.transform.position.x + i, terrain.transform.position.y + j), Quaternion.identity);
                 clone.transform.SetParent(terrain.transform,false);
             }
         }
     }
     
 }
   

Problems are :

• To generate button grid i need to loop with i and j + 25 (size of one button)

• Base position grid is 0,0

• I would like to center the grid because I can choose the size X and Y

• How to make disapear buttons who are in right up corner when i select one button.

Thank you for your help.

Sorry for my bad english.