this answer is based on knowledge from when my grandparents passed away and from looking into some holy books.
the term unveiling is a secular term and we dont actually unveil the stone. nevertheless after the stone has been put in place there is a minhag to go to the Kever, preferably with a minyan.
the following is the list of Tehillim customarily said and in that order, 33, 15,17,72,91,104,130.
then we say the name of the deceased following the letters in 119, follwed be the letters ????. (just the name and not the parents’ name)
then some say Kaddish followed by Keil MOleh Rachamim, some say Keil Mole Rachamim and then Kaddish. (i think more correct is Keil Moleh Rachamim followed by Kaddish.)
i have seen people read out loud the text on the stone but i dont know the source.
then one can light candles, say personal prayers, etc.
may we only hear of Simchas
???? ????? ???? ???? ?’ ???? ??? ?? ????