28 is not alot it maybe just the one rat , some times you can tell if there are young by the various sizes of the stools i did a rat job with my mate the other day an we were ankle deep in them we found a nest put his bedligton in who dispatched two one ran and one made the mistake of thinking he was safe in some pallets my mate got him with a 9mm shotgun great little tool for rats all in all theres probably up to twenty around the place so as i say 28 ain't much, have you tryed proofing the house ,they must be getting in somewere, if the keep coming back, the building works have got them on t