Good evening Adam and welcome to the Events Calendar forum!
Thank you for your interest in our products.
We’ll be glad to answer your questions.
I want to use your plugin on just 2-3 sites but sites that are in a multisite environment. Do I have to buy a Multisite license?
I believe you will find all of your answers here: https://theeventscalendar.com/knowledgebase/multisite-license/
Simply put, you can totally buy single licenses or a business license should you want to.
Our plugin will then need to be installed at a subdomain level, not multisite.
Let me know if that helps.
Have a great day!
Geoff B.