I had a very similar experience when I was interviewed for a science position at a small liberal arts college. The audience consisted of a small number of students though, (about 5), and a lot of faculty members including the dean (more than 10)!
To begin with, the only adjustment I made to my normal teaching style was that I prepared a self-contained lecture, i.e., I talked about everything one needed to understand the lecture without assuming they had any prior knowledge of the subject presented. I.e., I briefly explained the mathematical background needed to follow the lecture, the physics background, etc. To prepare the lecture I consulted with YouTube and Udemy lectures on other subjects because usually they do a good job of preparing self-contained lectures. Moreover, I always use Wikipedia to find interesting trivia on a subject to inject into my lectures.
Now during the actual presentation, I assumed that I'm the one in charge of the room (it's a psychological trick I use when I teach), so I didn't care about the audience in the sense that I wouldn't talk down to colleagues but I wouldn't disrespect anyone either. I stopped to ask questions, I discussed major points, and overall I kept the whole thing relaxed and to the point. In my mind, I was teaching a freshman class if that makes sense.
Finally, pick something you find interesting to teach (if you are free to choose) and enjoy the process. It's very important to have a bit of fun in any type of teaching situation anyway. Don't assume that colleagues will know every single thing you'll talk about. You'll be amazed about how happy people become when you talk to them about something they already know or heard about, but take it a step further. Good luck!
