They are all essentially the same thing. "There isn't" is a shorter way of saying "there is not" (we call it a contraction.. It is similar to "à + les = aux" but unlike French, it is optional, so it's really more like "tu as mangé" being written informally as "t'as mangé".
Whether you say "there is no" or "there is not" depends if you put an adverb in the sentence or not. For example:
There is no reason for war. (your phrase + a noun)
There is not (isn't) an easy way to find peace. (your phrase + an adverb)
It is the same thing with "they are", only are is the plural form of is (ils sont vs il a).