If you are under the per-participant pricing model, that is correct, as that would count as two participants during one minute.
If you are under the subscribed minutes, pricing model, that is correct too. Under that model, we charge for subscribed minutes (not published) so 2 subscribers equals 2 charged minutes for each elapsed minute of the session.
For SSM, the simple formula to apply when all users are publishing and subscribing is:
For n participants, there are n x (n-1) subscribed minutes per minute of conversation.
For example, a group of 5 people has 20 subscribed minutes per elapsed minute of conversation (session minute).
For per-participant pricing, the model is more simple, the charges are based on the number of participants in a video session, dynamically calculated each minute.