Normally, we go through the whips' offices to find out who will be on the subcommittee. In the chair's case, it's clear, but when it's one or two members from each party, it isn't always obvious.
You can discuss it now amongst yourselves, if you like, and perhaps even make a decision. You could put forward a motion specifically designating the members of the subcommittee. If the motion isn't clear, though, I'm not the one who will decide. In the committee's case, the subcommittee has to have five members. As I said, in the chair's case, it's clear. Then, it's one member per party, and that's not an issue for two of the parties.