One thing at least is fairly clear. In general, planning permission applies to a property and not to a person. You do not have to own a property in order to apply for planning permission.
The only way to fully resolve the planning questions would be to talk to the planning authority, usually the district council. If there is a question about whether changes are being made that do not have permission, the planning authority may take enforcement action. Although if permission has been applied for, the authority may be content to await its conclusion before taking any action. Even if it had not, the authority might have processed a retrospective application before taking any enforcement action.
Standards for councillors are uncertain under the new regime. However, it seems that the councillor you mention has a clear pecuniary interest in the matter, and likely that the chairman also does. If that is so, then if they were to involve themselves in parish council decisions on the same matter, they could be committing a criminal offence.