が必要 => need; necessary N4
必要がある => Need/Need to N4
得る => can; to be able to; is possible to~ N2
得ない => unable to; cannot; it is not possible to ~ N2
Ability
ざるを得ない => cannot help (doing); have no choice but to ~ N2
[要「よう」]するに => A. In short/put simply, B N2
Adjectival, Descriptions
要するに => in short; in a word; to sum up; to put it simply ~ N2
~をきんじえない(~を禁じ得ない) => can't help but; can't refrain from ~ N1
ざるを[得「え」]ない => Only A is left to do/can be done N2
(Not)only, (Not) even
[必要「ひつよう」]はない => It is not necessary for A to be done N2
Needs, Requirements
を[禁「きん」]じ[得「え」]ない => Can't help but do A, can't hold back from A (emotional response to something) N1
Will, Decision, Doing