ANSWER - It's a very important question and is anyone and everyone qualified to just give me an opinion and say oh yeah you know what they can hear you so you can go there and sit and have a chat with your your uncle and say uncle you know what aunt is troubling me a lot and so on really people think that you know the the dead perhaps they can hear everything and so on the truth is the only answers that are accurate given to us by Allah and Prophet Muhammad (saw).
As you correctly mention the Hadith of the dead hearing the footsteps of those who have come to bury and so on the truth is we know that when a person dies the functions, worldly functions of these organs is complete and over now it's connected to Allah, a different form and a different way. Allah allows them to hear certain things like footstep and does not allow them to hear certain things.
If Allah (subhanahu wa'ta'ala) has said clearly that the footsteps are heard, we believe the footsteps are heard and according to us the footsteps are heard because the Hadith says that and we stopped. Right? similarly when we say the Dua when entering the graveyard. The narration says they hear that? how they hear it I don't know Allah says they hear so now someone says well if they can hear the Salam, why can't they hear everything else? why can't I go and talk to them?
The reason is, let me just give you one example: you owned the radio so you'll understand the radio has so many stations you can tune to, so many stations but you tuned to one, when you're tuned to one you can only hear what's on that, one no matter what's happening on all the other ones, you cannot hear them so whatever is according to a certain tune on a certain frequency you can hear it that is explained by Allah and in the Hadees.
If I go and I say the Dua when entering the graveyard, it's on a certain frequency but the minute I start going and I start speaking about you know your son is troubling me, people do this? that's ignorance and people start asking questions and say you know I need help and you know this I really need you to assist me, guide me and so on that all that is disallowed in ISLAM so one might say well how is it disallowed, i say look it's the wrong frequency altogether, that's my way of explaining it so it's there in the Hadith as you said the slippers or the sandals and whatever you know is heard the footsteps.
As for Prophet Muhammad (pbuh), the Hadith makes it quite clear that anyone who has greeted me and and I respond to the Salam. How exactly that's done I don't know? it's not explained to us? I believe exactly that and I stopped at that but does that give me the right to start talking about so many other things and complaining, NO! we would stop exactly where that Hadith stopped. you go you do read the Salam, you follow the way the Sahaba did it and that's what happens.
Allah knows best