Is it permissible to fast for the missed days and then give charity for them all at once after completing the make-up for all the days, or is it obligatory to give charity for each day on the day of its fasting?

If you delayed making up fasts without a valid excuse, and you were aware of the impermissibility of delaying, then you have sinned. You are obligated to repent, make up the fasts, and feed one poor person for each day of delay. It is permissible to feed the poor before making up the fasts, concurrently with it, or after it. However, it is better to do so beforehand to hasten the clearing of your conscience.