You are going to be limited in what you can do, just because of the sheer volume of rabbits. It sounds like they are being fed the cheapest, “filler” food possible, again… Most likely due to cost with such a high number of rabbits.
What is going on with the rabbits? Are they being bred as pets, for show, or with the intention of “using” them in some way? The reason I ask is not to upset you (or other members), but because in some locations there are different “minimum requirements” for animals based on what their purpose is.
I think at this point, your only option would be to get the local authorities involved. Even if they investigate and find the conditions to be “minimally” acceptable, there may be a limit on the number of rabbits allowed on the property.
Any friendship that is there needs to come secondary to the welfare of those animals. Are you willing to file a complaint with animal control?