Please tell me the meaning of the sentences
Wintour mused in the three-minute clip.
Does it mean Wintour kept silence for three minutes and then began to talk.

"I think the two duchesses, the young duchesses that they have in Britain – the Duchess of Cambridge and the Duchess of Sussex – are going to keep the royal family afloat quite frankly," Wintour dished.
Duchesses in the sentence are the current British princesses.
What does "keep the royal family afloat quite frankly" mean?

Thanks for answering.

Question

Please tell me the meaning of the sentences
Wintour mused in the three-minute clip.  
Does it mean Wintour kept silence for three minutes and then began to talk.

"I think the two duchesses, the young duchesses that they have in Britain – the Duchess of Cambridge and the Duchess of Sussex – are going to keep the royal family afloat quite frankly," Wintour dished.
Duchesses in the sentence are the current British princesses. 
What does "keep the royal family afloat quite frankly" mean?

Thanks for answering.

Answer

"Mused" means to talk about in a happy way.  So it means during the three minute clip, she was talking about something in a relatively happy (or amused) way.  
"To keep afloat" means to keep in good conditions.  So that means that the two duchesses are keeping the royal family in a positive state or condition.  It's often used in terms of public opinion or economics. 
I hope this helps!

Answer

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Answer

"quite frankly" appears to be modifying "I think." So made more readable, it would be

"In my honest opinion, the two duchesses are going to be helping the royal family to survive."