Quite honestly, from what you say, the parish council is engaged in a lot of nonsense.
First, the parish council (or its chairman or clerk) has no power to instigate an investigation into an alleged breach of the code of conduct or to require a councillor to attend any meeting. Anyone can make a complaint to the Monitoring Officer, but that is all they can do.
Second, if a complaint is made to the Monitoring Officer, what will happen is that the complaint will first be considered as to possible validity. Only if it is regarded as potentially valid will the principal authority's Standards (not Scrutiny) Committee make a decision as to whether it should be investigated. If it is investigated by someone selected by the Monitoring Officer, it will eventually go back to the Standards Committee for a final decision.
Under the current regime, the Standards Committee has no power to impose the kind of sanctions mentioned in your question. It can take steps such as arranging for the "miscreant" to receive training, for a conciliation process to be instigated, or for a change to the procedures of the parish council. The recommendations are not necessarily limited to the "miscreant". So far as I know, the Standards Committee does not have the power to impose these actions, although it can aim to use the power of publicity to encourage compliance.
Note that all meetings of Standards Committees are open to the public. Consideration of breaches of the standards are never decided behind closed doors.
The only circumstances where sanctions would be more severe would be in a case involving criminal behaviour by a councillor, and that would likewise not be investigated by council members or clerk.