I guess I’m just kind of upset because they essentially branded me as a bad person for wanting to discuss this more deeply without giving me much to go off of

Oh, I totally get that, and that's why I wrote my initial paragraph.

They are trying to guilt you. Things are very uncertain for everyone, and they were not expecting a global crisis when you moved home last January.

They probably want for things to be vaguely fair and equal between you and your brothers (but with some sexism in terms of labor type), and that's impossible to calculate given how strange the situation has been over the past 6 months. They want money and are deeply ashamed of it, and they don't know how to deal with that either.

At the same time, 300$ was an extreme lowball unless they inherited the house without a mortgage with a modern well and solar panel system and you're putting in 20 full hours a week for them.