I can't say for sure about sewing patterns, but the copyright that holds for knitting patterns, it is a violation to copy it and then sell the original. You can copy patterns for person use. Meaning one to mark on while you are making the product, and you don't want to cut/write on the pattern.

If you copy it and then sell the original, you might as well have sold the copy- you are still in possesion of the pattern, which means you can use it, and so is someone else.

Generally you can share patterns. I can lend the patterns to a friend, but she can't make a permanent copy- and while she has them, you don't have them. That's the key. In theory, "Working copies" have to be destroyed after use.