(1) The faculties cease to function after death. However, there is no hindrance if Allah gives a dead one the power and sense of hearing and he hears.
(2) It is proved to do salam while entering graveyard according to sunnah. If someone does any bidah work, it is obviously wrong.
(3) Ask those people who are educated to mention the hadith as well as the comments of commentators of hadith, then in-sha-Allah, you shall be replied in detail.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband