People are usually not grateful to be corrected constantly, no matter what the subject.
If I had given birth to five single children and one had died, the answer to “How many children do you have?” would be four. The answer to “How many times have you given birth?” would be five. I would assume that family knew the story and would not need endless reminders. There’d be no need to discuss the matter with strangers unless I were really keen on underscoring how terribly special I was.
I am wondering what the effect on the four surviving multiples would be to be constantly reminded that one of them was lost, as if they were obliged to remain in a continuous state of mourning for one they had never known. I would think it might frighten them and make them feel vulnerable. If it is necessary to refer to them in the aggregate instead of as four children, I think I would consider their feelings first.