1.1. Bill is so clumsy. He has no manners
1.2. There is something in what you say, but he is an orphan and had no one to teach him.
2.1. Look at Neil’s feet! How can she wear such down-at-heel shoes at a party!
2.2. It’s all very well for you, but she has nothing else to put on.
3.1. Your friend can’t manage to get ready for the entrance exams all by herself. It’s no use trying.
3.2. I disagree with you there, I must say. Anyway, she has no one to help her.
4.1. Peter is leaving for the North Pole. Isn’t it great?
4.2. As for me, I’m all against it, but it seems there is nothing to be done about it.
5.1. Betty always seems to be awfully buzy! She says she has a lot of work to do at home.
5.2. Just the reverse. She is quite free and has nobody to take care of.
6.1. I have had a quarrel with Helen, as you know. I think it’s she who is to blame and I’m not going to apologize.
6.2. I think you are thoroughly wrong. She’s done nothing to offend you.
"Anyhow" should probably be "anyway" or "in any case" (sounds a little more natural, I think). If you mean "excellent" about the North Pole trip, say "great". "Isn't it fine" sounds too close to "Is[n't] that fine?", which is a way of asking permission. Otherwise, except for a single typo, all of your sentences are perfectly idiomatic, particularly in the way you handle the negative+infinitive construction. Very well done!