Possible Clues:

• Crucial core
• Core family member having upset top couple and me, royally
• Clue sun awkwardly as centre of orbital system
• Heart of uncle, possibly Uncle Sam
• One's positive setter will flip about clue that's been edited
• Uncle out to get us -- that's the heart of the matter
• Star's upset over cryptic clue's focus
• Scientific center?
• Central point of hint university dropped in students' union
• Atom’s core