Some good advice here imo. At 18/19, the lads are too old to play against NWC U18s, but could either play against student sides or Mens League teams. Either way, I suggest that you speak with John McMullen at the RFL, who has an interest in both areas.
What age group are we looking at? The NWC link provided is for 7-12s, but I suspect we may be talking about older players. If you confirm the age group, I will provide the relevant contact details.