I think it depends on what you're looking for. If you have a particular back story thought up for them and it doesn't fit with any of the established families, you can write your own and just connect them.
For example, for Ira, I felt pretty particular about her paternal line and their history going back several years, so I wrote an EFB for the Ilyins. But I was less particular about her maternal line, and Dylan was kind enough to let me insert her mother into one of his established families and connect that way.
In response to your second post, I think that could make sense! :] Depending on their wealth/status, you might want to consider what lines of work the paternal line was involved in before her grandfather started the business, and if the business is responsible for their current status, or how it might have influenced it.