To get the second pair of eyes, the AR on the far side should take a position in line, so they can see offences the referee cannot. The one of the referees side marks offside for the side not putting in. If it goes against the head, then you worry about the side putting in.
The TMO if there is one can use spider cam if it is there to look for props boring in.
Ensure all referees and ARs take a scrum training course before each season.
Make sure they all are looking for the same things.
I would have a meeting now and tell all the coaches that from next season you will do the following:
Actually penalize props not taking the bind, even before the ball is put in.
Penalize pushing before the ball is in, hookers not ready to hook and scrum halves feeding.
Remind them that deliberate offences can be yellow cards on the first offence, and the threshold for repeated offences can be two.
And my current bugbear, do the pre match brief before the match, not after the scrum goes down.
If you have given them the brief, there is no need to repeat it, if they did not listen, you have the whistle.