بسم الله الرحمن الرحيم
It is good to do isal-e-sawab for those who have passed away in your family. But it is not correct to specify first or last Thursday for the same. You can prepare food and feed it to the poor and needy ones without the specification of a date or day. Do not recite surah Fatiha or any other Surah on the food and do not consider it necessary. It is separate corporal prayer to recite the holy Quran and do isal-e-sawab and it is financial prayer to feed and do isal-e-sawab; so you should not combine them together.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.