When your aunt files papers to become your dad’s legal guardian, the court is supposed to notify your dad’s close relatives about the possible new arrangement—and you will likely be
on that list. It is then likely that a judge will ask you and some of the other people who are close to your dad for your opinions on his needs and the best way to care for him.
On the chance that the judge does not hold a hearing that requires your presence, you might want to find out who will be attending—and make any specific concerns you have known to him or her.
Finally, consider having a heart-to-heart talk with your aunt about what she intends to do to care for your dad—and how you can help.
There’s an informative article about the basics of this legal arrangement in this article on this site, “How a Conservatorship, or Adult Guardianship, Works.”