I did my research and ok so..

Dorea Black’s maiden name was Potter and she married into the Black family. She is the great aunt of Sirius Black, and even if James isn’t her descendant here’s how dis works:

Tonks is her great great niece

Dorea Black

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Sirius Black

Sirius is Tonks’s second cousin once removed or something, and Tonks marries Remus making Remus and Sirius related

Teddy marries Victoire, who is related to bill, who is related to Ginny who marries Harry

SO ALL THE MARAUDERS (minus Peter) ARE INTERRELATED

Thanks to (mostly) Dorea Black and Teddy Lupin

Who cares if it was after they died (cri), they’re hanging out in heaven where Remus and Sirius are years younger, Tonks is vibing with Lily and they’re all related now