1st question: No but you should have a Staffing committee normally composed of 4-5 councillors including the Mayor and Deputy mayor which handles anything confidential to do with staffing but the costs of staffing overall, even the individual amounts each job role gets, are not confidential. Check your financial regs, phone your clerk or check with the county assocaition.
2. Check your HR policy. Every council has to have one. I would suggest that unpaid work expeirence for family or friends OK as long as there is a policy regarding it in your HR policy, but any paid positions must be fairly recruited, candidates shortlisted, interviewed by a panel normally with at least one councillor and the clerk, appointments approved by the staffing committee, and noted by the full council. Again check with your Local ALC if not sure.
3. This is down to your Staffing Committee to sort out. The staff members concerned should have a procedure they can report to the Mayor/Deputy Mayor, a staffing meeting is called, a Greivance Committee is formed by the Staffing Committee, looks into the complaint and disciplines the Clerk if appropriate, according to your HR Policy.