Your friend should be able to join your tribe on a F2P account. He would not be able to be the tribe leader for any measurable length of time so you could not hand the tribe over to him and move on and make another. You must have him in sight, targeted and select invite from the tribe menu to invite him to the tribe. He would then receive a message box saying he was invited to join and giving him the option of joining or not.
If you find this issue still continuing, please submit a help ticket via the scroll with the question mark in the lower right hand corner of the in game screen.
I am also sorry for the delay in the response, the holidays have limited the staff support. That is no excuse, we should be more timely and I will endeavor to do so in the future. Again, my apologies.
Thank you for returning to Xsyon and we hope both you and your friend have a great time and stay playing for many years to come.