Of course judgement is not something anyone(not just nurses) should be doing, but education is a critical part of nursing. Educating on the benefit of discussing between the patient and family on whether they would like to complete end of life papers/POA/DNR/living will/whatever is important. We discuss that with every single patient who is admitted into my hospital. The honest truth is you can die from a routine gallbladder surgery so these forms are important to discuss with patients. Educating honestly on the pathophysiology of the conditions the patient has is something nurses do every day. Educating in a straightforward manner that a patient has risk factors for x/y/z and that is why they are getting this medication or that treatment, etc. If there is something we don't know we should be honest about that too, and yes, stick with facts.
When my family member was unexpectedly hospitalized as a young adult with TIAs and a heart condition which needed OHS, one doctor came in and told my family she was at risk of heart attack or stroke at any time. My family hated this doctor at first - he scared them with how he talked, and they thought him cruel because of it. However, they came to realize they liked the doctor the best because he was honest and was trying to prepare them for what may happen. Its not easy to say that a patient is very sick, but its unethical to lie or omit information to give false hope. A lot of it is in how you word it. Its one thing to say 'your family member has no chance', and its another thing to say "Your family member is very ill which is why we are closely monitoring him in the ICU. He has X condition which means Y, you have opted for treatment option Z which has potential complications ABC from that which we are monitoring for. Has the patient discussed with you his thoughts about what he would want if he should ever be in a situation like this?" Just the facts, ma'am.
I've had to make the call that a family should come in to be with a patient who was tanking. Again, wording is key. You don't word it "Your family member is going to die, you need to come in now", you word it that "Your family member is not doing well, we are not sure what the outcome will be, you should come in now to be with them." Were I to wait for the doctor the patient may have been unconscious or dead before the family got there.
There's no easy way to do a lot of this, but its part of our job as nurses.