(2) If daughter in law had done some nakadri when his father in law was alive so now after his death how she should seek mafi from marhumin?
(3) While sending isal-e-sawab we should make niyat for specially for one person for whom we want to send or it is better to send it to all who are dead from Adam (AS)?
بسم الله الرحمن الرحيم
(1) Yes, by the order of Allah they feel and reply our salam as well.
(2) Do istighfar for them extensively.
(3) It is correct if you do isal-e-sawab for any of them or even for the whole Ummah.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.