If someone's own family has issues with and turned away from someone, would that be a big red flag?

Absolutely. For instance, I recently learned that Cathy, our lovely problem tenant, who likes to trash talk everybody she knows, does not get along with her own daughter, and lied to me about her daughter having her own phone number and email address in order to limit my communications with her. In return, her daughter had a few very choice words for her.