I think the background spot is blowing out too much in the first photo. You should get a dimmer for that shop light. The sheet you are using in wrinkled too and it ends up looking like, well a wrinkled sheet. I agree that they are too dark, especially when contrasted with the spot on the background, it makes the subjects feel even darker. I think the spot works the best in the third image though. I would like it to go a touch higher so it could separate the top of her head from the background a little.
I think they are a good start and you just need to keep playing around and study portrait photography guidelines some more (there are a lot). I feel a lot of the framing and camera height doesn't quite work, but with some minor adjustments it could.
I think a lot of people have been rude to you to. You have thick skin and I guess that is good for the internet. If someone just wants to comment "I don't like it." they should probably skip commenting, because it doesn't help the person asking for feedback at all, and it probably makes the person feel bad a little. IMO these crits really are not about if you like something or not, it's almost irrelevant. The goal is to articulate what you think is successful in the images and what isn't, and why--from a technical and conceptual standpoint. I know a lot of people are new to talking about these things, but I hope people realize that saying, "I don't like it." compared to "I don't think this works because..." will get across the same idea, but one is a little more useful for the presenter. It takes a lot of courage to post creative work; it is a very vulnerable position to be in.