I find it very difficult to express condolences, for the same reasons given in the OP. I still have to bite the bullet occasionally, as I work in a nursing home. I keep things brief and be as kind/professional as possible; I’m not in a role where I’d be directly supporting family members who have just lost someone, but my manager is. I’ve seen a few different reactions, too. Never anything really negative or angry but if it did happen, I know it’s about the other person’s pain, not me.
As said, it does depend on the relationship you have with the individual(s) and how they deal with that grief, which you can’t really know for certain either. Some people appear to be handling it well in public but can be falling apart in private, after all.