And why did not a single member of her family, even Gertrude, dare to sign an affidavit stating that she was Franzisca?
Curious and curiouser.
Kind regards
Chat Noir
It makes sense to me that they wouldn't. She could have been in a lot of legal and financial trouble if she were exposed as making a false claim. They didn't want to cause any pain to her, or themselves, so they backed out gracefully. Imagine too how upset she'd be at them, and then they'd have to drag her home, kicking and screaming, hating them? She would likely have served time for her false claim, and been responsible for the costs of it. She may have gotten off on an insanity plea, but then she'd have been put away. Also, her supporters could have faced charges.
Felix was quoted as saying, 'if she is my sister, I won't have to be responsible for her, will I?" so this WAS on their minds. They were afraid of being stuck with some of her expenses, or having to support her for the rest of her life. It was best, as Felix later said, to 'leave her to her 'career' as Anastasia.' That way, she'd at least be provided for for life, she'd always find someone to take "Anastasia" in, but nobody wanted poor Franziska.

Also, you'd be surprised how fast some 'family' will turn their backs on you if they think it's going to inconvenience them in any way for any time, or even worse financially(personal experience) But I really think they felt it was best for all of them PERSONALLY (though not the courts, or the world in general) if she continued her charade. She really was backed into a situation where she really never could admit it even if she wanted to. She had too much to lose. When she married her husband John Manahan, he made her sign a paper swearing she was Anastasia!