How much antenna gain is required to close the link between the router positions that currently cannot communicate. Is this a practical antenna?

The table below shows the distances between router locations shown in the diagram.

Position 1	Position 2	Position 3	Position 4	Position 5
0 meters	120 meters	215 meters	215 meters	120 meters
	0 meters	100 meters	160 meters	100 meters
		0 meters	70 meters	100 meters
			0 meters	90 meters