Is it part of the Sunnah to recite the Shahadatayn (the two testimonies of faith) to the deceased at the grave's edge after burial, and does the deceased hear and see those around them?

The fundamental principle of تلقين (talqin - instructing the dying) occurs during the throes of death, based on the Prophet Muhammad's (peace be upon him) saying: "Instruct your dying ones to say 'Lā ilāha illallāh' (There is no god but Allah)." As for instructing the deceased after burial, it is permissible according to the preponderant opinion among scholars, though it is not obligatory by consensus. It is considered to be a practice narrated from a group of Companions. Thus, some imams, like Imam Ahmad, permitted it, others recommended it, while some disliked it, believing it to be an innovation. Therefore, there are three opinions regarding it: recommendation, dislike, and permissibility. Regarding the deceased hearing, scholars have stated that the deceased generally hears the speech of the living, but it is not necessary that this hearing is continuous; rather, it may occur in some situations but not others.