Can We use this game engine please ?

If you'd like to, you are allowed to. You can use whatever engine you're happy with. What we want to make clear is that our people (our instructor and student volunteers) really only know Unity very well (a bunch of people have used a few different engines, and we're good at figuring things out, but we only focus on Unity). So we will try, but we may not be able to help you when you run into problems. If you're good with that, we're good with that.