If the tires are not older than 4-5 years(some say up to 7) and they are rated to cover the weight of the trailer, you should be good to go.
I always OVER TIRE anything I have, if it calls for a 14 ply, I'm looking for an 18 ply. If it wants 12"...it's getting 15, if it will fit.
My 2 cents
Remember that a 12 inch tire is really rolling the faster you go. hold to 55 and under. Like others have said replace if 5yr old regardless of tread left. bearings really take a beating on thes small wheels as others have said so have them repacked.