chess - Checkmate all the kings #1

The purpose of this puzzle is to find the minimum number of moves to checkmate all the kings.

RULES

• You are playing as White and you can make as many moves as you want before Black's turn.


• During your moves you can take any black piece except kings.


• During your moves your king can not be in check position.


• At the end of your turn all the black kings must be check mate : if Black can make one move that ends with one king being safe, you don't win. Note that this one move can't be a king moving to a threatened position.


• One piece can be used in multiple checkmates (you don't have to take all the king, just to checkmate them)

Examples :

This is a valid ending position because both kings are check mate (A king can not move in a check position to defend another king)

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This is not a valid ending position because one of the king is not checkmate

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This is a valid ending : a single piece can checkmate 2 kings

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I have tried to make this first puzzle easy to introduce the concept. I will make harder similar puzzles later, feel free to create one yourself too...

Answer

I got a quick answer but not sure how good it is.

1 rook to g6(2 moves), the other rook at a8(1 move)
1 knight to d5(2 moves), the other knight to e5(3 moves)
total 8 moves