Both Riveras holding the one thing that's keeping them together.

General Hospital: Are you well enough protected here? That would be my crowning glory wouldn’t it? Nikolas loses his mother and I lose Nikolas.

General Hospital: So it is true? I missed you.

General Hospital: I know that I may be crossing a line, but may I remind you, so are you with Katherine.  You’re repeating yourself, Alexis. 

Actually, yes.  One of Mikkos Cassadine’s brothers, Tony, was romantically involved with/engaged to Alexandria “Alex” Quartermaine, Edward’s niece.  Both died in 1981 when they walked in the ice chamber of Mikkos’ weather machine.  Nikolas Cassadine was married to Emily Bowen-Quartermaine, Alan’s adopted daughter.  Both of Mikkos Cassadine’s illegitimate daughters Alexis Davis (born Natasha Alexandra Mikkosovna Cassadine, raised as Alexis Davidovitch) and Kristina Cassadine were both involved with Ned Quartermaine (formerly Ashton).  Alexis actually left Ned at the altar.  Even though Alexis’ middle daughter Kristina is a Corinthos, Ned originally said he was the father in order to protect the child from Sonny and mob violence, which killed the original Kristina.  For about the first year of life, Kristina Davis was raised as a Q in the mansion.  Alexis had lost custody after killing Luis Alcazar and faking DID, so she posed as the Q butler.  Sam McCall, a Cassadine via  mom Alexis, married two Quartermaine heirs: twins Jason Morgan and Andrew “Drew” Cain.  She had children by both, Danny (Jason) and Emily Scout (Drew).  Stefan Cassadine fell in love with Chloe Morgan, a Quartermaine cousin (actually a distant to Q matriarch Lila) and one of Ned’s wives, who was murdered by his brother Stavros.  As for non-romantic Quartermaine/Cassadine connections, I think Helena Cassadine coerced Tracy Quartermaine into working with her at one point.

But I could be wrong.  My previous wish was for Nathan’s dad to be a more evil Cassadine than Victor.  I had hoped for Stavros for a few reasons: it would piss off Helena, give the delicious Robert Kelker Kelly more to do than crazy, and give Nikolas more good Cassadine relations other than his son and the Davis girls.  But the writers killed off most of the Cassadines.  My second choice would have been Valentin, before we actually met him.  He was supposed to be so evil and such a threat that Helena feared him and we could have had a Spencer/Cassadine team up.  But then we got the dark gray and charming Valentin, as played by James Patrick Stuart, who is married to Nathan’s cousin/sister.