Sportmenship

[Texas Aggie]

You need to have a meeting with them and tell them:

1. There will be no abusive or even negative comments on the officiating.
2. There will be no negative comments allowed against a team member or an opponent, whether its their child or otherwise.
3. There will be no negative comments voiced about the coaching. If they have an issue, they need to take it up with you privately.

Essentially, all comments will be positive or there won't be any.

These people are acting like children themselves and as such, they need guidance. I suspect that if you lay down the law, that will take care of 90% of your issues. The other 10%, you'll just have to deal with (I'd advise removing them from the gym), but you'd have to deal with that anyway.

If they take their child off the team, in my view, that's a problem solved.