Sounds feasible, especially if your 6 employees are paid.
If the codebase for your project is very simple, then yes, one programmer should be enough. But keep in mind that the programmer is the one that glues everything together. You could have the best Graphics designers in the world working on your game, but if something happens to your programmer then your game development will probably come to a halt. It will be imperative that your one programmer codes in such a way that others can make sense of it in a worst-case scenario.
I also feel like Unreal is a bit overkill for a point-and-click adventure -- lots of visual-novel/point-and-click games use Ren'Py or modified RPG Maker MV.
But on the other hand, using Unreal might be a very good choice to make your game stick out from the crowd.