SW's Miltanks's Healing Milk

[Charizardian]

I have a Secret Wonders Miltank in play and two damaged Benched Pokémon. I use Healing Milk and flip two heads. Would I be able to remove 3 damage counters for each or would I have to remove 6 from one of them? If I can remove 3 damage counters from both, am I also able to remove 6 from just one if I want to?

 

[PokePop]

You only get to choose one Pokemon, just like it says.