It's quite difficult really, I found the problem similar in my CCF; there's people like me that ultimately want to join the forces, and lots of people that are there just as a laugh and to have fun. Obviously there's nothing wrong with that, but when you've got the muppets who just waste time and ruin it for others then yeah, something's got to be done. Personally, I'd let the CO know that cadet X Y and Z are always casuing problems, then he can see it for himself and take the action he sees fit; I've found that the Officers are far more ready to do something when they're sure that the action they're taking is right, rather than relying on someone else's word for it (ideally they should take action if you tell them, but I've found that realistically they just can't be bothered.) Don't send them to the CO too soon for some minor problem, or you won't really have anything to do if others get out of hand, as they'll get used to a little telling off. But at the same time they've got to know that they can't just piss around. A lot of it, of course, depends on your CO's attitude.
How many camps with testing boards have they attended?
Have you spoken to them to find out why they are not making any progress and being disruptive? Is it actually their fault?
Is there any reason why they have been unable to complete their required APC subjects that is beyond their control? Ie: Shooting not available? Records lost? (Bloody Westminster!)
Because if thats the case, it's not surprising they mess about and have no respect.
Really, these cadets cannot be blamed entirely for their behaviour or lack of achievement. Your DC and Coy are just as culpable in not getting a grip, pushing these cadets along and motivating them sufficiently. It's easy to maintain discipline when cadets are motivated, keen and have an active training program.
Sitting around at Rec level for 3 years whether by choice or due to circumstance beyond the cadets control should not be allowed.
Realistically, there is little you as a Cdt L/Cpl can do. This sounds like a policy issue* and a failure to instil discipline, standards or deliver training in your County/Coy