E.g. if we have a meeting with 20 members where we discuss influencing policy, do we need to report all their names, and will all their names then be publicly visible?

It is important to note that the one (organization) doing lobbying is required to register and report.

The consultant lobbyist or the designated filer for an organization must identify any coalition to which the client or organization belongs if the purpose of the coalition is related to the lobbying activities engaged in by the client or organization. Consultant lobbyists and designated filers for organizations are required to list the name (business name) and business address of each member of the coalition.