This is not at all uncommon. The second hen has gone broody, and she is merely taking advantage of a nest full of eggs. It's as logical to her as the number "two" following the number "one".
This does complicate things. I'd say there is a 30% chance of things working out splendidly, that the two hens will co-incubate the eggs and co-parent the chicks when they hatch. Those are not the best odds, though.
Things are more likely to take a disruptive turn, and eggs will end up getting broken, and if any survive, chicks may be fought over and injured. It's best to deal with this matter now in a decisive way.
How important is it to have two broody hens incubating two nests full of eggs? Are you in the process of seriously breeding and expanding your flock? Or is this nest full of eggs and the broody sitting on them something that has happened all on its own without much thought to it on your part? It's time to make a decision.
If you want two broodies, make two nests. They ideally should be protected from other hens who are laying daily eggs, as this activity can result in damaged eggs and dead embryos.
If you do not want any new chicks or if you only want the current eggs that are being incubated to come to full term, then break the second broody. If you do not know how to do that, we can instruct you.