High Gain Antenna Recommendations

Hello, I am seeking specific high gain, omnidirectional, +9dBi/+12dBi antennas, purchase recommendations: brand and model. I will need a total of 6 as I have 2 routers (so please no 100US$/antenna but somewhere under the 200US$ total cost. Asus RT-AC66U broadcasting on 2.4GHZ & 5GHz but on 802.11nac only Buffalo Giga Airstation Nifty WRZ-G144 broadcasting on 2.4GHZ on 802.11g only Asus uses RP-SMA connectors and I posted images for the Buffalo connectors I am completely ignorant about antennas and I am afraid to buy the wrong antennas which may hamper some functionalities such as mimo, dual band, concurrent TX/RX etc I would very much appreciate specific brand & model advice as I have no idea about antennas price/quality, thank you.

What kind of distances are you anticipating. What environmental obstacles are present? Do you anticipate the remote machines needing good through-put for frequent streaming and downloading?

Doug, Thanks for helping me. - Distances: Max 10m - Obstacles: Plaster walls, thin, wooden frames. Max 3 walls between router/client. Ceilings (& under floor) filled with insulation, cables, metal air ducts. 15 radios broadcast on the 2.4GHz WiFi band. All ch mixed. 2 networks broadcast stronger signals than my own 802.11g network. - Setup 1) 802.11g only 2) 802.11n (2.4GHz) only 3) 802.11n (5GHz) - Separate SSID - Only one DHCP server issues IPs: - Routers/client within 3ft on horizontal plane ( can use narrow diffusion band) - 802.11g is used by Media Centre (Vudu 1080p during peak congestion times) which has only 802.11g radio - 802.11g overwhelmed by 2 stronger signals (neighbors) - clients will use adapters w/ high gain antennas, if necessary. - extra network planned on 802.11 ac - clients will use 802.11 ac adapters as soon as available. Already tried: - moving routers locations, - changing channels, - higher/lower positioning - rotating antenna angles - laying cables impossible - home plugs power line adapters impossible bcs: 1) already too many radios & 2) electric cabling on different breakers Do you need any other details to give me specific advise? Pls consider that I can replace the Buffalo (and obviously ASUS) antennas by myself but I don't think that I can replace the adios. Again, thanks in advance for helping! Really needed!