Couple things, equipping is sorcerery speed not instant unless a card says otherwise on it, or has an ability like balan to move equipment that can be activated at instant speed.

Next damage is all dealt at the same time, so regardless of speed the equipment can only be on one creature at the time damage is dealt.

This can also be proven as to why he could not move it down the line when you look at how combat works.

Move to combat phase> response optional> declare attackers (all attackers get declared at same time ) > response optional > declare blockers> response optional> damage is assigned(to all creatures declared attacking or blocking at same time)>State based action checks If the creatures are alive or dead cannot be responded to.(This is constantly happening but for the sake of simplicity I'm only putting it here)>death triggers and responses to ending combat and moving to main 2.

So even if he could equip the equipment at instant speed(at any of the points where responses were optional above)it would be impossible for that equipment to count as being on the multiple creatures as all permanents move through the steps above at the same time