No, there is no such word as „kins“. The word „kin“ doesn’t change if referring to one person or more than one: „He is my kin“, „They are my kin.“ But, „kin“ is a very colloquial word, and sounds rather sloppy and regional to me. I don’t use the word myself. I never have actually used the word. I understand it. It’s just not in my vocabulary. There are many better words out there than that that mean the same thing. I believe it comes from the rather archaic „kinfolk“, a word that is fairly out-of-date.

Often you hear the phrase ‘kith and kin’, which is essentially friends and family. It is at least Old English, and Germanic or Norse in origin, which fits with your book’s theme.

Hi there! “Kin” is a word that typically doesn’t change or become plural. Whether a sentence is saying “he was her kin” or “they were her kin,” the number of people being counted as “kin” doesn’t make it plural— kind of like “sheep.”