Posts have a slug (that’s the last part of the URL), and it must be distinct, even if posts are in different categories.
If your only worry is SEO, don’t worry. Google sees the URLs as distinct, and Google is used to dealing with URLs that have a suffix on them, and has no problems with it. The keywords in the URL are still the same and have the same value.
If you still want to change this, you could manually change the slug when you create the post, or you could hook into save_post and change the slug to be street-casa. But there is no need.