Typically a FHA home sale should take the same amount of time as a conventional sale. My guess is that there was a problem with the title that had to be cured before closing which held everything up. It sounds as though there was a breakdown in communication between the buyers, agents, sellers, and attorneys. I know of agents who have had very long closings, but everyone knew what was taking so long and why, and agreed to keep waiting. The final walk-through only needs to be attended by the buyer and their agent. The seller's agent should try to be there in the event of a discrepancy. As far at attendance at closing - it varies with the region and the buyer/seller involved. I rarely attend closings, but ask my clients ahead of time if they would like me there and follow their wishes.
Six months to close is a LONG time! I'm going to bet that there was a problem with the title that had to be cured before closing could happen. This sounds like an attorney paperwork issue and not an FHA banking issue. Good luck!