If a guest wants to bring an extra person to an Experience they've booked with you, they can do that. 
Your rights as a Host
It's up to you, as the Host, to decide if you can accommodate any extra people. If guests show up with extra people, you have the right to turn them away. Hekaya does not offer customer service to people who don't have an official reservation through the platform, and any liability waivers you may offer your guests won't apply.