What is the ruling on a girl accompanying three young men, fearing to advise her or inform her parents due to their excessive trust in her and their desire to marry her off?

It is an act of loyalty to your friend to advise her and warn her about those relationships and their severe consequences, either directly or by insinuation. If she does not desist, then threaten her with informing her mother or other family members. If she persists, then inform her mother or another person who can stop her, provided that you mostly believe that no great harm will result from that.