This account is very much complimentary to My Brother's Keeper, I suggest reading it in order to understand/care about what happens in this excerpt. Go check it out!
On the paternal side Leonard Crouch/Lawson is the grandson of Charis Black/Crouch and Caspar Crouch, who are more closely related to the Weasley and Longbottom clan. His mother had been one of their three children, canonically dying before 1995 and for the sake of the Lawson's, before Elizabeth or Noah were born. I've given her the name Terebellum in recognition of being a would-be Black member. Since there isn't much about ANY of Charis/Caspar's children except possibly that their son had been Barty Crouch Sr. and due to the daughters' ambiguity I decided to have Leonard's mum be disowned as a blood-traitor, as although she married an unnamed pure-blood she did not have the same views on blood supremacy as the others. This makes Leonard, a pure-blood, second-cousins of such characters as Sirius, Narcissa, Bellatrix and the Weasley's and his children (Noah and Elizabeth) their distant cousins. Maternally, Constance Meadowes/Lawson had a Muggle-born father and halfblood mother, her sister being Dorcas Meadowes who had canonically died during the First Wizard War and had been killed by Voldemort himself. Here's how this looks in relation to Noah and Elizabeth:
Paternal great-grandparents: Charisa Black and Caspar Crouch
Paternal grandparent: Terebellum Crouch/Lawson (Canonically unidentified) (died before '95)
Distant and or closest cousins: Weasley's, Longbottom's, Black's, Crouch's
Maternal aunt: Dorcas Meadowes (died during First Wizard War)
Paternal great-uncle(Possibly): Barty Crouch Sr.
Parents: Leonard Crouch/Lawson (Black descendant) & Constance Meadowes/Lawson
Although the Crouch line has said to be gone extinct (officially) it does not explicitly say that neither of Caspar Crouch's daughters had children (just that they died before '95) and because Leonard's mother had been shunned/removed from the House of Black I figure that the Crouch's would also -being just as discriminatory as the Black's- not count Terebellum as a Crouch anymore or her offspring as well as the fact that neither of the girls could pass on their family name (though having close ties to the ministry, save Barty Jr., they aren't nearly as open about it in my opinion). Not to mention the Black line has gone extinct, but we know for a fact that it actually lives on through the Malfoy's and through Nymphadora's (she had also been removed from the House of Black) line.
I've put a lot of thought into this family tree, trying to make it as accurate as possible in accordance to what JKR has given us about the family lines and seeing as there is A LOT of intricacies it can be kind of hard to fit OC's in there, the only person I've had to REALLY squeeze in however is Constance as she is for this story in the original Order with her sister, when in reality it was just Dorcas. But honestly even then I think it works well and as far as OC family backgrounds go it is very solid and doesn't stick out NEARLY as much as some of the other's I've seen.
Terebellum: 'gives a fortune, but with regret and disgrace, cunning, a mercenary nature and repulsiveness.'