Is it obligatory to make up for missed Ramadans and pay the expiation that results from them, taking into consideration ignorance of the obligation to fast and illness that makes fasting difficult?

You must make up for the Ramadan fasts you missed after puberty. If you cannot be certain, then act based on your best estimation until your obligation is fulfilled, for the Prophet, peace and blessings be upon him, said: "Allah's debt is more worthy of being fulfilled." Your ignorance of the obligation to fast does not negate the need for making up the fasts, although it may remove the sin. Along with making up the fasts, you must pay an expiation (fidya) of feeding one poor person for each day you delayed making up the fast without a valid excuse. However, if you were ignorant of the impermissibility of delaying the make-up fast, then no expiation is due from you. If you are able to make up the fasts, then that is the obligation, and you may make them up on separate days or delay them. If you are unable to make up the fasts due to an illness from which recovery is hoped, then wait until you recover. If the illness is one from which recovery is not hoped, then the obligation is to feed one poor person for each day, as Allah, the Exalted, says: "And upon those who are able to [fast, but with extreme difficulty] - a ransom of feeding a poor person."