In zou when the crew were discussing sanji being a vinsmoke we see robin saying she heard of the name but couldn’t place it but to the side we saw brook with the ……. Speech bubble which shows he knows something but didn’t say anything.

In another panel brook states the vinsmoke name is a name then sends a chill down his backbone.  
So there is definitely something there.

Now 52 years ago the rumbar pirates were attacked by some rival pirate and it resulted in them all dying even brook who came back due to his df.

It was stated that the ship was broken in a way that it made steering impossible which shows it was a calculated attack and that the weapons they used were poisoned to ensure no one survived.  
The poison makes me think it was a precursor to Reiju who is known as poison pink.

So either by chance or because they were payed to do this, the vinsmokes attacked brooks crew.  
If the flashback goes that far to this attack I think we will see judge as a toddler as he is 55 currently and we would see his father and sanji grandfather.

It is ironic as brook and sanji have so much in common,  they are both the crews registered perves, both of them are vastly dedicated to their crafts.  
They are the crew mates Luffy requested the most because at the start he wanted to find a chief and a musician first as food and music are his top priorities.  
Both also understand what it means to grow up in starvation and in royalty but reversed.  
Sanji was a prince who ran away from home got caught in a storm and ship wrecked for a year and nearly starved to death

Brook crew up in poverty and struggled for food saying his family essentially starved to death then he was adopted by the prince and eventually got ship wrecked for 50 years.

This flashback will end with the reveal it was sanji grandfather who killed brooks crew, but brook obviously doesn’t blame sanji which is why he never brought it up before as he didn’t want to make sanji feel even worst about where he came from by having it be revealed it was his family that killed brooks 3rd family.

Sanji grandfather killed the rumbar pirates