When an invitee registers for an event with a guest from that moment on, they should be treated as one. If the host changes their registration, somewhere the user should be alerted there is a guest. When the host is seated, the guest should be seated along with them. If a host is re-seated, the guest should be re-seated, too. Or, at least a system alert should appear to the user warning them of a guest. As it is now, if you seat a host, the guest is not brought along nor is there a system alert to the user that this person you are seating is bringing a guest so do you wish to seat them, too? And, if you move a host or a guest, the system does not alert the user they are no longer seated together.
I find this to be true with seating groups, too. A user goes to the trouble of creating a seating group but the system does not preserve the group and ensure they are seated together. I understand the need may arise when the group needs 'broken'. Then put in a system alert when one of the group members is re-seated without the others. "You are re-seating an event registrant who is part of a group. Do you wish to move the entire group to the new seating location?"