Other members are allowed to come and speak at committee; however, they would not be allowed to vote if were not officially substituted in. Even if we were to draw parallels to the House, I would say that members are free to come in and out of the House and speak, whether it's in question period or afterwards. If their name is on the list, they come in and they have a speaking slot, regardless of whether or not they stayed in the House chamber the whole time.
That's just to draw that parallel. That's not how committees function, but we take a lot of parallels from the chamber itself as well.
In terms of the substitutions and members sitting in, Justin, would you want to clarify whether they can speak or not?