Can some examples of royal families in the west marrying brothers to sisters be given?

While there are historical aspects to this question, you may want to consider X-posting it to /r/AskAnthropology or else /r/AskSocialScience as this is also a question that would be fitting for those subreddits.

Humans actually have evolved specific things to avoid incestuous relationships. One experiment found that women instinctively prefer the smell of sweat of men that they do not share certain genes with, which helps prevent attraction to individuals whose genes are too similar to their own (note: the test was NOT run on men). A 2007 Scientific American also notes that other mammals have similar adaptations:

By mixing siblings in a litter, for example, scientists have shown that animals that grow up together appear to avoid mating, whether genetically related or not, largely based on recognizing specific smells.

So it's not really a question of when humans made a conscious decision that incest was wrong. Instead, we're genetically programmed to avoid it. I do not have source material/expertise to elaborate further.