"If you two want to help you can. But I need to get these dormant fire spirits awake. I'm not sure if Remey's alchemy fire spirit or of the other fire spirit will come in but we'll leave the door open." Walker didn't want to stop them from coming if they wanted to. He knew that both of them were imperative to the spirits having similar friends.
There was also the theory that if they used their educationist skill to trach more people the spirit mark skill they could have other alchemists that could use the alchemy fire spirits to control the heat. It wouldn't be as good as Rmeey who could use the alchemy flame but it was still fairly amazing in its own right.