father is in prison.
mother of the child doesn't want the fathers family to have anything to do with him.
child is only 8 months old so there's no relationship between the grandparents and the child.
grandparents have tried seeing the child but mother denies any contact.
Family Law Attorney
In general, so long as no competent court has determined the legal parents to be unfit as parents, the legal parents has the ultimate authority to determine who may see their minor children.
Depending on why the father is in prison, his parental rights may be restricted.
The grandparents can review the facts with local attorneys to see what options the grandparents may have. It may be that they have no legal option.
Family Law Attorney
No, grandparents cannot file anything in court for visits. What can be done is for the father to pursue contact with the child. Obviously a lot depends on why he's incarcerated and for how long. Many prisons do what they can to make family visits reasonable for the children. 8 months, though, is still really young to be taking to a prison (and may not work if the prison is far away).
If there's little likelihood that the father will be able to pursue visits, he should still take classes in prison, especially parenting classes and anger management (if that was an issue). Also he should make a point of acknowledging holidays and birthdays (if there's no court orders prohibiting contact with the mom). Even though the child is too young right now, if he's going to be away for awhile it'll help for him to have established a pattern of reaching out to the child.
Last, as the father makes an effort to maintain a relationship with the child, it's important that he not be super-demanding about having his parents involved. Guilt trips and threats of court action never work. He should try to involve you in conveying cards, photos and gifts. Don't push the mom too much either---courts will not back you up.
Child Abuse Lawyer
Sadly, both counsel are correct. Grandparents' "rights" have been largely obliviated over the years. The only time grandparents may have "rights" to visit would be if a child was in the custody of DSHS under a dependency proceeding. So long as there is a fit parent with custody, he or she has sole discretion in this realm.