Bio dad subpoenaed my mom

My mom has had guardianship of her nephew for 11 years (since he was 6mos old).

Bio dad (allegedly) is subpoenaing my mom to court, not sure if it’s for custody or visitation. My brother (11) has been assigned an attorney. My mom has no idea what to expect. Bio dad and bio mom lost custody due to drug addiction and we have no idea if they are clean or have a stable home. After my brother was born they had twins who were taken at birth and eventually adopted to a nice family.

There has never been a true effort of trying to see my brother. They have gone through other family to go behind my mom’s back to see him. My mom nicely asked them to go through the court to get visitation because his safety is important. They never did it.

Now we are here years later. What should we expect from the court date? Can my mom request a dna test? Bio dad never signed the birth certificate.

Does he still have rights? Can he be granted custody of my brother after all this time? Bio mom isn’t asking for anything but I know they are back in a relationship. She’s probably pressuring the dad to do this.