If the cats are medium- to long-haired, you may not be able to see the testicles! And they may not completely 'drop' until the cats are about a year old.
I've never had to litter train a cat, even feral ones. I always just took them to the litter box one time, and just plopped them in. They seemed to know instinctively what it was for, and never 'went' anywhere else. Maybe you can entice them to the area with a tidbit of smelly cat food or fish.
I strongly suggest that you have them spayed or neutered as soon as possible. Otherwise, you may have several dozen half-feral cats within just one year! And it may help prevent some undesirable behavior, such as urine spraying. Your local Vet or Humane Society may be able to offer suggestions and the loan of a cat carrier to transport them for the procedures.