I've never met a person named Iselinde or Isengard, and they sound very old fashioned, so I'd be surprised to meet anybody with one of these names who's younger than 60 - but you can still find them in some good name books.
Traditional Old High
German names like Iselinde and Isengard are very old fashioned in Germany at the moment, and I'm sure it'll take a while until they will return. Nowadays, at least in the north of the country, old Low
German, Frisian and Scandinavian variant forms of those old fashioned names are really modern again, e.g.
Isa, Iska and Iske which are Low
German pet forms for "Isen-"-names.
/
Satu
http://www.nordicnames.de/