The obvious place to start is with Captain Marvel herself. Or... Photon? Or perhaps Pulsar? Or maybe I should call her Spectrum? Monica Rambeau is only the second person to assume the title of Captain Marvel in Marvel Comics publication history, as well as the first woman to do so. Following her introduction in Amazing Spider-Man Annual #16, Monica became a major character during her time as a member (and leader) of the Avengers. Soon, Monica would fall prey to the greatest foe in comics history: marginalisation. Monica would leave the Avengers after being depowered and left as a near-dead husk (Avengers #294).
After regaining powers, Monica made mostly guest appearances apart from two single-issue Captain Marvel comics in 1989 and 1994 before relinquishing the heroic identity to Genis-Vell, the son of the original Captain Marvel. Monica also takes on the name Photon in the same story (Avengers Unplugged #5) before next appearing in Avengers (vol. 3) #1-3. So, presumably she's still called Photon in the MC2. If you've been keeping up with these MC2 Family Tree entries, you already know the usual point that the Main Marvel Universe diverges into the MC2 Universe is.....somewhere around 1998, maybe. Oh, boy. This stuff is confusing. We'll come back to it later.
Monica's parents both make their debut in Avengers (vol. 1) #246. Maria Rambeau is a seamstress and Frank Rambeau is a retired fire chief for the New Orleans Fire Department. While Frank is supportive of his daughter's super heroics, Maria had difficulties letting Monica risk her life after years spent worrying about her husband in his dangerous occupation.
Derek Freeman is an FBI Agent who encountered Monica several times during her time with the Avengers as Captain Marvel, at first in an official capacity but soon in a romantic context. Derek first appeared in Avengers (vol. 1) #263 and at some point prior to Captain Marvel (vol. 2) #2 had deduced Monica's duel identity. It's also in the latter issue that we are introduced to Derek's nephew, Raymond Washington.
Duane Freeman (brother of Derek Freeman) was the Federal Security Liason assigned to the Avengers who first appeared in Avengers (vol. 3) #4. As anyone who's read previous MC2 Family Tree's knows, the usual 'cut-off' point for characters and events from the Main Marvel Universe existing in the MC2 is generally at some point around late 1997-1998, roughly coinciding with the beginning of the MC2's own publication history. Though Duane Freeman dies off-panel and behind the scenes in Avengers (vol. 3) #49, it is entirely possible the events leading to his death did not occur in the MC2. I'll definitely have to do another post someday covering my theories of how much of the Main Marvel Universe post-divergence can be included in the MC2's own history.
Given that Derek is Raymond's uncle and Duane is never stated to have children, in addition to Raymond already being 21 years of age in Captain Marvel (vol. 2) #2, it's logical to assume that Derek and Duane have another as-yet unseen older sibling.
And now for the character that ties these two families together: Blacklight. First appearing in A-Next #9, we learn little about Blacklight during her fight with the Soldiers of the Serpent. However, in the same issue we are also introduced to Kendra Freeman, a young woman on the committee for the Neighborhood Pride Street Festival which was attacked by the Soldiers of the Serpent. While it's not established on-panel, 'word of god' from co-creator Tom Defalco here confirms the familial relationship. Additionally, the Official Handbook of the Marvel Universe: Alternate Universes 2005 lists Blacklight's real name as Kendra Freeman. As Tom's original answer doesn't specify which Freeman brother is the Kendra's father, I reached out to Ron Frenz, the characters co-creator who clarified that it was in fact Derek Freeman.
So there you have it! Two families brought together in the Might MC2 Manner! Hoo-Ha!
Until I run out of characters to mine for MC2 Family Tree's, I remain
frogoat