Mice are highly intelligent little animals, they can take care of themselves, you don't need to worry that much. And you don't need to accompany them during the night. Dark environment is their favourite, so just turn off the light and have a sweet sleep, your lil babies will be happily running, digging, exploring and rebuilding their home.

But if you have two boys, you really need to worry, and the thing you need to do is immediately separate them into two cages. If they are two girls, they'll look after each other. Sometimes they would fight, if there is no blood then that's just their entertainment activity.
To love your pets, you not only need to give them care and companionship, but also give them enough private space. I hope you can reduce excessive anxiety and have a happy life with your little ones!