It is dangerous for an outsider to judge. If a councillor (or their family or associates) has a pecuniary interest in a council decision, then the councillor in question cannot participate in the decision. The new enforcement regime is untested, but serious breaches are now a matter for the criminal law. That means the stakes are high and one must be cautious about making allegations. But if you are concerned, then a reasonable step would be to raise the matter with the senior legal officer of the higher level local authority - usually a district council.