Based on your description I'd say you should talk to a professional who has experience in this kind of setup and can come onsite.
EIRP tells you what's the actual transmit power of the antenna in milliwatts, calculated from radio transmit power, cable loss (signal loss on the cable between the radio and the antenna) and antenna gain. SNR is signal to noise ratio, which in your case is 7. That's way too low for any usable connectivity.
Antenna gain is what it is, not adjustable. Neither is the transmit rate per se, that depends on the transmit power of the AP radio and the distance from the antenna. The further away you go, the lower goes the RSSI and transmit rate goes down with it. Your option there is to check whether the AP radios are set to 100% transmit power. If not, increasing will improve the reach.
On that distance you need high-gain directional antennas. Just seeing the other antenna isn't enough, the Fresnel zone needs to be free. Any obstruction there will directly affect your signal. So you need to consider the antenna installation height as well, which brings the cable loss into the calculation. And yet another point is how much radio interference (both WiFi and non-WiFi) is in the area.
Radiolabs has online calculators for power output, free space loss, Fresnel etc. You can input the relevant values see what you get. But that's only an approximation, real-life situation can be very different.
Now there might be some kind of amplifiers I'm not aware of that could improve the situation. But applying those again means contacting a professional in your area.