it must be very unlikely that the next of kin come and have a look on PPRuNe.
I seem to remember at least two separate threads in the last six months or so, on two separate accidents, where someone representing the next of kin registered on PPRuNe specifically to take part in the discussion. That was partly to express their distaste about certain postings, and partly to obtain some background information about the more technical aspects of the accident.
Actually it was hinted that the next of kin later got in touch with some of the more experienced pilots on here and discussed some aspects of the accident in great depth, in private.
Furthermore, threads on here are also read and indexed by the Google bots (and other search engines). If a name of an accident victim or the aircraft registration appears on here then you can be sure that it is one of the first ten hits in a Google search within two or three days. And that means that you can be pretty sure that the next of kin will be around to see what's been posted within, oh, a week or so?
So, in contrast, I find it very likely that the next of kin will eventually read what I write in an accident thread, and I personally try to write my responses (if any) so that the next of kin are not offended, and with respect for the deceased.