Nadia Diamondstein and Noah Gershom are not related, although their lives are connected in a couple of interesting ways. Nadia's paternal grandfather, Izzy Diamondstein, chose to marry Margaret Draper late in life at the senior community of Century Village. Nadia's father, Allen Diamondstein, was supposed to be the best man for his father Izzy. When Allen Diamondstein broke his ankle right before the wedding, Noah Gershom, who happened to be staying with his grandparents at Century Village at the time, was asked to stand in for him as best man for Izzy Diamondstein.
In addition to this connection, Nadia Diamondstein's mother, who has recently divorced Allen, her husband and Nadia's father, is a dental hygienist who works for Dr. Gershom, Noah's father.
Although Nadia Diamondstein is not related to Noah Gershom, she is related to Ethan Potter as a result of the above-mentioned marriage of Izzy Diamondstein and Margaret Draper. Ethan is Margaret Draper's grandson, and, as noted before, Nadia is the granddaughter of Izzy Diamondstein.