My dad was sick for many years and he couldn't fast Ramadan and we were paying for every day he was not fasting after that he passed away some people said we must fast for him the months he didn't fast so please tell us what to do.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If your father had missed fasting due to an incurable disease or due to his old age, then in this case, you have to feed a poor person for every day he missed fasting as you did during his lifetime. Therefore, you are not obliged to do anything after his death. On the other hand, if the disease was curable but it continued till his death, then in this case, you are free from any obligation and the feeding of the poor person that you had done is considered only a good act, you will surely be rewarded for that.

Allah knows best.