Sure, two hens can sit on the same eggs. In fact, it's pretty common for hens to share a nest. But there's a catch: the eggs need to be fertile for this to work.
If the eggs are infertile, then it doesn't really matter how many hens are sitting on them. The eggs won't hatch no matter what.
But if the eggs are fertile, then two hens sitting on them can actually help to incubate them. The hens will take turns sitting on the eggs, and the warmth from their bodies will help to keep the eggs at a consistent temperature. This can improve the chances of the eggs successfully hatching.
Of course, there's no guarantee that two hens sitting on the same eggs will actually result in baby chicks. But it's definitely worth a try if you're hoping to increase your chances of success.