Yes lovebirds can get bruising on their beaks, much like how humans can get bruising on their fingernails. Bird beaks are actually made up of pretty much the same substance as our fingernails, only thicker. The bruise will grow out until it's eventually gone. If you notice that your bird is showing discomfort eating, give him soft food to eat until he is feeling better. Of course if it is really bad, then a vet appointment would be necessary.
I don't know if you are referring to one or your birds having a bruised beak, but if you are then I hope he recovers soon. Good luck!