Yes, they are aphids. The white things are the discarded skins of aphids. Yes, they will harm your plant. You can approach dealing with them in two ways. Douse the plant with soapy water - that won't kill them, just wash them down and they will hike back up. You will have to repeat every day probably. If the container is small enough and you can put it on its side in a tub or sink, you can wash them down the drain.
Poison them. I use Insecticidal Soap as it will kill them without killing me. You will have to repeat spraying periodically.