You’ve gotten very good advice so far. I am a nurse too, used to work on cancer floors and did a stint in neuro ICU. Nutrition and hydration are a must. Remember Terri Schiavo. She was murdered by starvation.
Beyond that, the best thing to do is get honest answers from the doctors. If there is no chance of recovery, you are not obligated to continue extraordinary measures, but you can if you choose to. That means things like ventilators, or surgery to insert any assistive devices like trachs or stents or anything is up to the family if the patient can not give their consent. You are not doing wrong by either refusing them, or choosing to use them. But if a feeding tube or central IV site is needed for nutrition/hydration, then that must be put in. At least, that is the way I have understood the Catechism. Think about JPII, he chose to have a feeding tube, but no other extraordinary measures.
Will be praying for your family.
ETA: With some types of heart failure, excessive hydration will actually worsen the problem, but nutrition still needs to be provided. In other words, no extra IV fluids, but some type of food, whether through the IV or a feeding tube in the stomach, should continue.