Yes, that's where I took the Swiss thing from, I haven't heard that word before. As for the technical term, to me that sounds like one of these artificially degendered forms that are en vogue to day. For anyone who doesn't knows it: 'Geschwister' comes from sister, it is kind of like sisterhood, the other term is 'Gebrüder', which is outdated now. (Yes sisterhood would be 'Schwesternschaft', I can't think of an English grammatical equivalent. Maybe something like 'sistered', the participle to sister describing the set of people you are sistered to.)

The feminist crowd just perceives a common male word as gendered and a common female word to be not.