How do I deal with Inferi?

When Dumbledore is trying to drink the potion and the Inferi keep coming up the hill and dragging you into the water, is there a way to keep the Inferi back and stop them from dragging you down the hill? So far I am only able to grab a drink of the potion, then wait to be dragged into the water. This means it takes me a while to drink all five cups. Can I hold them back in any way so I can drink them faster?

I used Reducto (the orange spell) to constantly blast them back. That keeps them away long enough for Dumbledore to finish his drinking game.

Another option is to hit them with Augmenti. The spray of water blasts them into pieces and gives Dumbledore the time he needs to drink the glass of water.

Also, whenever you are grabbed by the Inferi, if you switch to Lumos Solem, they let go of you for a brief amount of time, which is long enough for you to jump and run far enough away from them that you can switch back to a different spell that will destroy them.