If these are the complete facts of the case, you and your friends have most likely committed the crime of trespass. This assumes that the house, though empty, actually belongs to someone. It also assumes that you did not intend to take anything.
If you and your friends entered the house without force and you did not intend to take anything from the house, you are not committing the crime of burglary. If you entered the house with the intent to take things (even if it turned out there was nothing there to take), you are guilty of burglary.
Even if you entered the house without intending to take anything, and even if you did no harm while you were inside the house, you are still guilty of trespass. Whenever you go on to someone else’s property without permission, you are guilty of trespass. Your intent does not matter and neither does the fact that you did not cause any damage.