Generally, the natural parents will have a presumptive right to custody. Only in cases where the parents are found to be unfit, or there are exceptional circumstances, will third parties be granted custody. At any time after a divorce, grandparents may petition the court for visitation rights.

There is a complete list of the Domestic Relations Forms available in PDF format.  To view and print forms, you may be required to download the free Adobe Acrobat Reader software.  

Also see Article from the Family Law Advisor on Maryland visitation and custody.
AARP Grandparent Information Center

If you're interested in mediation, here are some national organizations that can help you find resources in your area:

American Bar Association:
http://www.abanet.org/dispute

American Arbitration Association:
http://www.adr.org

Academy of Family Mediators:
http://www.mediators.org

Conflict Resolution Center:
http://www.conflictres.org