They have no right of way, one on another - אין להם דרך זה על זה
Summary:
The ruling of אין להם דרך זע"ז is based on the ruling of כל המוכר בעין יפה מוכר. By האחין שחלקו all the brothers are considered sellers and relinquish any rights in the portions that now belong to their brothers.
And if you wish I can say; this and that are from the outside - ואי בעית אימא הא והא מבראי
Summary:
A בית שער מגוואי is never desirable. Every חצר has a דלת. The flow of the answers is not symmetrical (first assuming the desirable option and later the undesirable).