What is your relationship with your neighbor? Can you speak with her about what you think, and ask her if she needs you to help her decide what she should do? Without her permission, you may just be meddling and getting yourself involved in the mess.
What is your relationship with the men? Is either of them friendly enough with you for you to give him advice without being considered nosy? Usually, such secrets come to light after a while, and all three of them can learn valuable lessons about respect and honesty in relationships. Meanwhile, stay focused on your path and don't let them distract you.