There are two solutions to this problem. One is to export the filesystem that holds the fonts from sirius to xeno . This is easy, especially if that filesystem also holds the X-server binary for diskless clients. But sometimes fonts may reside outside of the normal X directories on sirius . The manual page gives full details.
Full details are in the manual page for xset.
In the beginning X-servers relied on a host access list to decide what applications could talk to them. This is not very secure as it is based on IP addresses and it is possible for an intruder to pose as a trusted machine and gain access to the X-server. A more secure mechanism is the Xauthority scheme. Here the X-server generates and deposits an access token called a cookie in a secure location where the legitimate clients can pick it up to gain access. This is usually a file in the home directory of the user called .Xauthority and readable only by the user.