... I think you and your wife are intimidated by these people, and so is your father.
It's strange that he just sits and quietly listens to all their negativity. He could at least tell them the badmouthing and negativity aren't good for his health, OR everytime they start up he could ask them to leave and get assistance from hospital staff if necessary. Putting up with toxic behavior isn't a pre-requisite of being liked and respected.
I agree with this. I think your father is afraid that if he sticks up for you two then they will stop visiting him altogether and just make things harder for everyone.
I wish your father could realize that only HE can really put a stop to this. HE needs to be the one to tell them to knock it off. HE needs to notify staff of wherever he currently is that he really wants to see you. HE needs to tell his pastor/priest/whoever will be conducting his funeral that he wants you there as an active participant. HE needs to tell his lawyer that he wants no shenanigans with his will.
If you can't encourage him to do this, perhaps his pastor, the nursing home director, or someone else who is not involved personally can give him the courage to do what he needs to do, or at least make his wishes known, preferable in writing. Or at least on videotape.