In your situation you may get by with mounting rooftop antennas on each house in your group connected to even five watt hand held radios.
In other words you may not need a repeater. It would still need to be high above the roof of your house. It may not gain you anything over a rooftop antenna connected to your radio. Try that first.
20 miles is not that far for GMRS as long as you have line of sight between antenna. If the antennas can see each other they can talk. Even 100 miles or more. The challenge is to get your antennas high enough. That is how you maximize range. That is also why a hand held at street level in a suburban area may not have much range because of all the buildings and trees in the way.
I live on a hill facing the direction of most of my contacts with line of sight between us and 30 miles is no problem even with just five watts. More power can help at times however antenna height is more important than power generally.
The way repeaters work is they are usually mounted as high as possible like on a tower or mountain or tall building. They receive your signal and then rebroadcast it out over a wider area because they are higher and above most obstacles. You do not connect to them with a wire. Generally one repeater is used and as long as each antenna can see the repeater it can relay the signal between two or more radios.
If you are looking to be self sufficient then don't rely on someone else's repeater as it may be down if the power is out.
There are directional antenna's that concentrate most of the energy in one direction. Two of these can be pointed at each other for improved range in more difficult terrain or longer distances.
Keep learning before committing to gear, you will save some money. Radio requires a fair amount of experimenting to be competent with.
Good luck!