I think the Venn diagram should resolve as follows:

The three categories are:
Top left:
People who have famously been on trial (link to title: 'trials and tribulations')
Ian Brady, Ted Bundy, Charles Manson, OJ Simpson, and - in fiction - Josef K
('Famously' is key here - I'm pretty sure that if you dig deep enough you could find trials featuring people with the other surnames here, but none quite as high-profile as these...)
Top right:
Television sitcom families
Brady (The Brady Bunch)
Bundy (Married... with Children)
Royle (The Royle Family)
Simpson (The Simpsons)
Spencer (Some Mothers Do 'Ave 'Em)
Bottom:
People who have married into a royal family (link to title: 'jubilation' → 'jubilee' and a sense of celebration)
The British royal family:
Wallis Simpson, married then-Prince Edward (later King Edward VIII) in 1937;
Diana Spencer, married Prince Charles in 1981;
Sarah Ferguson, married Prince Andrew in 1986.
And one from Monaco:
Charlene Wittstock, married Prince Albert II of Monaco in 2011.
The central shared word is thus:
Simpson