The guild should be updated so that a party leader can pay the fee for a group
to use the trees.
This would be in a similar manner in how normal room exits, dim door, etc.
operate.
Since it would be a major addition, it's worth considering whether owners
should be allowed to have a separate pricing scheme/markup or the option to
enable/disable group travel along a link. However the amount of work in
implementing the latter option may not be justified.