Here's what you can do:
Find the Probate and Family Courthouse for the county where your family member lives. You can use this town look-up tool: Massachusetts - Where do I file?
BEFORE you file, have a lawyer check that all of your paperwork is filled out correctly.
File these forms at the same time: the Petition form, the Bond form, and the Clinical Team Report.
In some cases, the Court may appoint a lawyer for your family member.
Sources: Commonwealth of MA