Can felv+ cats survive spay/neuter surgery?vet techs or people with felv+experience?

friends in economic trouble moved to a rental where pets are not allowed.i now have their 2 felv+ cats,a male and female about a year old.both doing well so far despite leukemia.i would like to have these 2 spayed/neutered.can cats with this illness withstand surgery?how about routine shots-rabies and distemper shots-is this ok for them,or will it strain the immune system too much?i have an appointment for them at the end of the month,to have their operations.they are perky and happy and act normal,but they are thin.vet techs-is surgery ok or not?also,seems strange they were together one year,but the female did not get pregnant-are they sterile due to illness?any advice to keep these 2 happy/healthy is appreciated.they now have a home for life with my family and we will do whatever we can for them,medically,and as beloved pets.