You won’t solve this problem with a 2 hr online NALC ‘course.’ That’ll be a complete waste of time, money and effort.
If, as it seems, you have 20 year served Cllrs it’s just as likely that the root of the problem is disengagement and disinterest from the electorate which has (assumed) allowed many successive uncontested elections returning the same inadequate and poorly behaving Cllrs which enables the perpetuation of bad habits and ineffective procedure as new entries to the council (probably through repeated cooption) are inculcated with existing habits and behaviour.
It’s just possible I’ll concede that you ‘could’ have 20 yr served Cllrs because they are so ‘good’ at the role that they warrant multiple terms of office - don’t sound that way from what you’ve described though.
The enduring solution to problems like this is invariably to drastically uplift public awareness and engagement in council business. Find a way to let people know their behaviour will and is being viewed more broadly - audio / video record and broadcast council meetings for a start!