I don't see why your amendments to change 2016 and 2017 to MFJ would not be accepted. Of course that will only entirely correct the excess contributions if your modified AGI when your and your spouse's incomes are combined is under the limit for those years ($184,000 for 2016 and $186,000 for 2017).
Amending 2016 and 2017 would not affect your 2014 and 2015 Forms 5329, but you might still want to just send all of the 2014 through 2018 forms together.
Yes, the revised calculations are correct.
Your 2020 Form 5329 will show the $11,000 distribution being subtracted from the $11,000 excess carried into 2020, resulting in a $0 excess for 2020 and beyond.
Your 2020 Form 8606 will show the $11,000 distribution on Part III and your basis in Roth IRA contributions will be subtracted with the result being $0 taxable.
