Saint-Germain-de-Tallevende and La-Lande-Vaumont were two communes that incorporated into one and combined their names. A commune is similar to what we would call a municipality and may comprise several villages. La-Lande-Vaumont had 18 villages by itself.
There were several men called Saint Germain, but one is known in English as Germanus of Normandy. Chapelle Saint-Germain at Querqueville in the Manche departement is dedicated to him. It is one of the earliest surviving places of Christian worship in the area, according to several tourist information sites.
I don't know any meaning for the word Tallevende. There are at least two other places in the same area that include that name: St-Martin-de-Tallevende and Les Vergers Tallevende, an English-owned orchard. There was a cook by the name of Taillevent who was born in Normandy. He served several French kings in medieval times and authored an early cookbook. Several restaurants are named after him. I don't know if he has anything to do with the place name Tallevende.
A "lande" is a wild place that grows prickly plants, sturdy flowering bushes and large ferns. A moor in England is similar. The thickest part of the landes are difficult to traverse unless there are paths worn or cut through them. They have a fragrance that I've never experienced anywhere else, and I'm not sure which of the plants or combination of plants create it.
I don't know and haven't found the origins of the name Vaumont. It is a surname that is found here and there. I have heard of an artist by that name and a character in a play.