My job puts me around a lot of accidents and deliberate stupidity that leads to death in many many cases. I’m consistently around hospitals, families, and family friends. Religion inevitably comes up in one way or another daily.

First off; condolences for everything you’re going through.
On their end; it’s their coping mechanism too. They likely just assume.

You can politely explain it to them. Typically…. 99% won’t question it, but be prepared if someone (or three) does.
You could also take the more subtle approach and find a tasteful anti-religious shirt and to wear and a book or two to just leave around. You’ll get some some looks, but they’ll get the point that you support it enough to be open about it.
Good luck. I hope all goes well for you both.

You might want to delete this copy of your post, since it hasn't drawn any comments besides mine here.