Two people worked on a plot for a rank that doesn't require the builder to fill the entire plot. I suggest that they both be allowed to rank up seeing as this method of team work would only work until they are both experienced because Architect requires a player fill their entire plot. My second suggestion is to allow either normal players or donators to use /p h <name> to teleport to other people's plots. This won't be an issue because if a player doesn't want them on their plot they can still /p deny them and it makes it easier to get to a persons plot for both parties because one person isn't being spammed multiple times for teleport request and the other person can still get to the plot even if the owner is offline.
They should also be an option to a plot being to allow this command, the default is to allow the command on one plot, but this can be changed to not to et out..