You typically need to place two bombs to kill them. Place the second shortly after the first and it will kill the Beetom on your way down. The remaining Beetoms can be safely killed from the ledge.

Requires:

{
  "enemyKill": {
    "enemies": [
      [
        "Beetom",
        "Beetom",
        "Beetom",
        "Beetom"
      ]
    ],
    "explicitWeapons": [
      "Bombs",
      "PowerBomb"
    ]
  }
}
{
  "enemyDamage": {
    "enemy": "Beetom",
    "type": "contact",
    "hits": 2
  }
}

Clears obstacles: A