Monster equipped with 2 Safe Zone then 1 of them is destroyed
Activate this card by targeting 1 face-up Attack Position monster on
  the field; that face-up monster cannot be targeted or destroyed by
  your opponent's card effects, or be destroyed by battle. It cannot
  attack your opponent directly. When this card leaves the field,
  destroy that monster. When that monster leaves the field, destroy this
  card.


Since Safe Zone explicitly mentions protection from your opponents card effects, it will indeed not protect your monster from a second Safe Zone you control, equiped to it.  

For your second question, the same logic applies. The monster may not be under your control, they are still your Safe Zone. So yes, all 3 cards will be destroyed.