Groups/Websites handling

Hi all. I’m quite new to Magento2, working on a project since 2 weeks more or less. I have to make, and I already made, two website for two different kind of customers(even if my idea was to use a single one with a groups handling). I just don’t understand, is it possible to set only one single group of customers for each website?For example, does make sense having a website for customers within only a customers group and one website for retailers just with retailers group? I apologize in advance if I was a bit confusing, but trying to get into a world that’s not mine (btw I’m basically a Java dev)