Hello Kyoung2120 - welcome to the Ubisoft Forums!
I am sorry to hear that you are struggling to connect to your friends in For Honor. Have you and your friends all checked your NAT types? If any member of your party has a "Strict" NAT, this may cause issues for you all when trying to connect.
I would recommend that you all run through our connectivity troubleshooting in this support article, in particular the portforwarding section, to try and reduce the impact of any connectivity issues.
Can you also tell me any additional steps you have taken to try and troubleshoot these issues with joining a group?