There appear to be some serious problems there - it's difficult to know where to start!
It is not up to fellow councillors (including the chairman) to decide whether a councillor should declare an interest. The new regime does, however, have few sanctions against councillors unless the matter is serious enough to count as a criminal offence. Declarations of interest should be recorded in minutes.
A council cannot lawfully meet unless three clear days' notice of the meeting has been given by posting an agenda in public. A council cannot lawfully decide anything that is not reasonably clearly spelled out as an agenda item. Decisions made by a council must be minuted, and citizens have a right to inspect minutes.
If you feel that the council is not working to proper standards, you can complain to the legal officer of the principal authority - usually the district council.