What is the ruling on making up for the days that were not fasted in Ramadan for two years, due to low blood sugar and circumstances of travel and work, and what is the method of expiation for those days?

As long as you are able to fast, even if only on some days of the year, you must make up all the days you missed in both Ramadans, whenever it is easy for you to do so. You are not required to pay expiation for delaying the make-up, because the delay in the first instance was due to forgetfulness, and in the second instance it was due to illness and undergoing surgery.