You do not need to worry about the priority date once he is a US citizen. Once he is a citizen, send the NVC a copy of the certificate and a copy of the I-130 approval notice and ask them to change the category. it will take about 3-4 months for him to have an interview once you pay the National Visa center fees.
It sounds like the government attorrey is wiling to re-paper your filing, that is to close it out and then reissue the notice to appear after you have the ten years. Your attorney should be discussing this with the government attorney.
Renouncing your US citizenship is a very serious matter and there is probably no getting it back. Do not take this step without thinking about it. If you need to meet your family, consider meeting in a third country where you can get a visa. Think about how difficult it was to get to this point.
Form I-751s are not as much a priority at USICS as I-485 applications. The normal processing time is about 6 months. Just be sure to keep the original receipt notice as that will allow her to travel and work. I often see them take 7 or 8 months. It is quite normal. If she does want to travel oversea before getting the ten year card, be prepared for her to go through secondary inspection on return - also quite normal.
Biometrics take a minimum of 30 days to clear unless you are in court and the office of chief counsel pushes it. therefore, I would expect 30-60 days for a work card or interview, depending on what you filed.
Your attorney knows your case best. However, you may want to consider a Congressional inquiry or inquiry through the USCIS Ombudsman office. Sometimes, a little pressure helps. Talk to your attorney first