Ask HN: Should you avoid taking pictures of elderly friends and family?
Don't they perceive it as an insult, as it could imply, "Let me take a photo of you before you die"?
My generalized opinion is to just be tactful and sensitive. They are old enough to know your intentions. They've already lost many of their friends. Get them to show you their photo albums and maybe take some pictures of their pictures or make a video of them talking about people in the pictures. Ask their permission where you may post the video you made, such as only sharing with family members privately via thumb drive or if big brother social media is ok. I prefer self hosted private family forums. Whatever happens give them a hug, it's worth more than anything you can say.
But to reply to your questions, the answer is yes - take photos but do it in the proper context
The most common social error I see when younger people interact with older people is that they treat the older people as if they're a special case or delicate flowers to be handled with kid gloves. Just treat them like the normal humans they are, the same as you'd treat anyone else.
I've had more than one friend die young and unexpectedly (not knowing that the last time we were in person together would be our last time), so if justification is needed, it is as simple as "Tomorrow is not assured, and any of us could be dead tomorrow. I would like to remember this, if that's okay with you." But, to each their own approach to life and interpersonal relationships. I appreciate the reply, so that I can better understand others.