The peak gain lobe is straight off the face of the side where the coax solders to so if you are holding the antenna with the coax in your hand and the cable in your hand the peak gain lobe you be hitting you in the face. The null, or low gain area, comes out the top of the antenna so if you were to extend the coax cable past the solder point that would be the direction of the low gain null or depression in the pattern.
If you are placing 3 of these antennas orthogonality is your friend. I would start by placing one antenna with the coax going down to the ground. The second antenna I would place to the left of the first antenna but rotate it 90 degrees clockwise to the coax is point away from the first antenna. place the two antennas 20mm apart.
The third antenna I would place to the right of the first antenna rotated counter-clockwise with its coax pointing away from the first antenna and spaced 20mm apart from the first antenna. This orientation should get you at least -10dB of isolation (S21 between antennas). If more isolation is needed increase the 20mm spacing between antennas 10mm more.