You can have 10 people in the stream on the Basic and Professional plan.
You can have 6 people in the stream on the Free plan, but up to 10 people can enter the broadcast studio, so you can swap people in and out if you’re doing a dynamic talk show.
The maximum participants you can have in the StreamYard studio on the Professional Plan is 12 total (including the host). You can move people in and out of the studio at anytime to accommodate over 12 people, as long as there are only 12 people in the studio at once.
Free: 6 people on screen, 10 people in the studio
Basic: 10 people on screen, 10 people in the studio
Pro: 10 people on screen, 12 people in the studio