Help save the strays

A year and a half ago, I found a starving cat outside my door, and my heart went out to it! His bones were showing and his hair was falling out, so I started feeding him. It turned out that he had two twin brothers. What sad little babies they were. Soon after, another cat came along, and then another, and then another. You probably get the picture.  Now, we have 20 cats, which includes four kittens.  We thought about taking them to the animal shelter, but  they are overrun and do not have room.  I cannot stand the idea of them being put down. They are all so sweet and funny, but most people do not want adult cats. I have asked friends, and they have also tried to find loving homes for these adorable cats, but no one is able or willing to take them on.  Now, with winter coming , we are concerned about them not having adequate shelter. People bring cats in and dump them off, but we are trying to help them out. I have tried talking to vets about treatments and getting them fixed, but trying to take care of 16 cats can be quite expensive. I hate to turn to the public, but I have exhausted all other avenues.  Any help that we can get to save these beautiful animals is greatly appreciated. Thank you for showing an interest in these animals.