How ridiculous is this? (Girlfriend’s family)?

I'm afraid that you gf has got to stand up to her parents. Either she tells them that she is not going to do as they say anymore because she is 21 and an adult or she just stops going home at 11 pm tells them that she is going over to your place and is thinking about getting engaged. If she doesn't do either of these things she will never break there hold over her and you will both end up parting from each other.